Sorry to drudge up an old thread.
I’m hitting the assertion in a Standalone build of a plugin (with no changes to the standalone window) since updating to JUCE 7.0.10.
This is the full stack trace on Mac:
juce::MidiMessageCollector::addMessageToQueue(const juce::MidiMessage &) juce_MidiMessageCollector.cpp:54
juce::AudioProcessorPlayer::handleIncomingMidiMessage(juce::MidiInput *, const juce::MidiMessage &) juce_AudioProcessorPlayer.cpp:412
juce::AudioDeviceManager::handleIncomingMidiMessageInt(juce::MidiInput *, const juce::MidiMessage &) juce_AudioDeviceManager.cpp:1171
juce::AudioDeviceManager::CallbackHandler::handleIncomingMidiMessage(juce::MidiInput *, const juce::MidiMessage &) juce_AudioDeviceManager.cpp:99
<lambda>::operator()(const juce::universal_midi_packets::BytestreamMidiView &) const juce_UMPU32InputHandler.h:85
juce::universal_midi_packets::Midi1ToBytestreamTranslator::dispatch<…>(const juce::universal_midi_packets::View &, double, <lambda> &) juce_UMPMidi1ToBytestreamTranslator.h:76
<lambda>::operator()(const juce::universal_midi_packets::View &) const juce_UMPConverters.h:175
void juce::universal_midi_packets::Conversion::midi2ToMidi1DefaultTranslation<void juce::universal_midi_packets::ToBytestreamConverter::convert<juce::universal_midi_packets::U32ToBytestreamHandler::pushMidiData(unsigned int const*, unsigned int const*, double)::'lambda'(juce::universal_midi_packets::BytestreamMidiView const&)&>(juce::universal_midi_packets::View const&, double, juce::universal_midi_packets::U32ToBytestreamHandler::pushMidiData(unsigned int const*, unsigned int const*, double)::'lambda'(juce::universal_midi_packets::BytestreamMidiView const&)&)::'lambda'(juce::universal_midi_packets::View const&)>(juce::universal_midi_packets::View const&, juce::universal_midi_packets::U32ToBytestreamHandler::pushMidiData(unsigned int const*, unsigned int const*, double)::'lambda'(juce::universal_midi_packets::BytestreamMidiView const&)&) juce_UMPConversion.h:222
juce::universal_midi_packets::ToBytestreamConverter::convert<…>(const juce::universal_midi_packets::View &, double, <lambda> &) juce_UMPConverters.h:173
<lambda>::operator()(const juce::universal_midi_packets::View &, double) const juce_UMPDispatcher.h:188
void juce::universal_midi_packets::Dispatcher::dispatch<void juce::universal_midi_packets::ToBytestreamDispatcher::dispatch<juce::universal_midi_packets::U32ToBytestreamHandler::pushMidiData(unsigned int const*, unsigned int const*, double)::'lambda'(juce::universal_midi_packets::BytestreamMidiView const&)>(unsigned int const*, unsigned int const*, double, juce::universal_midi_packets::U32ToBytestreamHandler::pushMidiData(unsigned int const*, unsigned int const*, double)::'lambda'(juce::universal_midi_packets::BytestreamMidiView const&)&&)::'lambda'(juce::universal_midi_packets::View const&, double)>(unsigned int const*, unsigned int const*, double, juce::universal_midi_packets::U32ToBytestreamHandler::pushMidiData(unsigned int const*, unsigned int const*, double)::'lambda'(juce::universal_midi_packets::BytestreamMidiView const&)&&)::'lambda'(unsigned int)::operator()(unsigned int) const juce_UMPDispatcher.h:58
void juce::universal_midi_packets::Dispatcher::dispatch<void juce::universal_midi_packets::ToBytestreamDispatcher::dispatch<juce::universal_midi_packets::U32ToBytestreamHandler::pushMidiData(unsigned int const*, unsigned int const*, double)::'lambda'(juce::universal_midi_packets::BytestreamMidiView const&)>(unsigned int const*, unsigned int const*, double, juce::universal_midi_packets::U32ToBytestreamHandler::pushMidiData(unsigned int const*, unsigned int const*, double)::'lambda'(juce::universal_midi_packets::BytestreamMidiView const&)&&)::'lambda'(juce::universal_midi_packets::View const&, double)>(unsigned int const*, unsigned int const*, double, juce::universal_midi_packets::U32ToBytestreamHandler::pushMidiData(unsigned int const*, unsigned int const*, double)::'lambda'(juce::universal_midi_packets::BytestreamMidiView const&)&&)::'lambda'(unsigned int) std::__1::for_each[abi:v15006]<unsigned int const*, void juce::universal_midi_packets::Dispatcher::dispatch<void juce::universal_midi_packets::ToBytestreamDispatcher::dispatch<juce::universal_midi_packets::U32ToBytestreamHandler::pushMidiData(unsigned int const*, unsigned int const*, double)::'lambda'(juce::universal_midi_packets::BytestreamMidiView const&)>(unsigned int const*, unsigned int const*, double, juce::universal_midi_packets::U32ToBytestreamHandler::pushMidiData(unsigned int const*, unsigned int const*, double)::'lambda'(juce::universal_midi_packets::BytestreamMidiView const&)&&)::'lambda'(juce::universal_midi_packets::View const&, double)>(unsigned int const*, unsigned int const*, double, juce::universal_midi_packets::U32ToBytestreamHandler::pushMidiData(unsigned int const*, unsigned int const*, double)::'lambda'(juce::universal_midi_packets::BytestreamMidiView const&)&&)::'lambda'(unsigned int)>(juce::universal_midi_packets::U32ToBytestreamHandler::pushMidiData(unsigned int const*, unsigned int const*, double)::'lambda'(juce::universal_midi_packets::BytestreamMidiView const&), juce::universal_midi_packets::U32ToBytestreamHandler::pushMidiData(unsigned int const*, unsigned int const*, double)::'lambda'(juce::universal_midi_packets::BytestreamMidiView const&), void juce::universal_midi_packets::Dispatcher::dispatch<void juce::universal_midi_packets::ToBytestreamDispatcher::dispatch<juce::universal_midi_packets::U32ToBytestreamHandler::pushMidiData(unsigned int const*, unsigned int const*, double)::'lambda'(juce::universal_midi_packets::BytestreamMidiView const&)>(unsigned int const*, unsigned int const*, double, juce::universal_midi_packets::U32ToBytestreamHandler::pushMidiData(unsigned int const*, unsigned int const*, double)::'lambda'(juce::universal_midi_packets::BytestreamMidiView const&)&&)::'lambda'(juce::universal_midi_packets::View const&, double)>(unsigned int const*, unsigned int const*, double, juce::universal_midi_packets::U32ToBytestreamHandler::pushMidiData(unsigned int const*, unsigned int const*, double)::'lambda'(juce::universal_midi_packets::BytestreamMidiView const&)&&)::'lambda'(unsigned int)) for_each.h:26
void juce::universal_midi_packets::Dispatcher::dispatch<void juce::universal_midi_packets::ToBytestreamDispatcher::dispatch<juce::universal_midi_packets::U32ToBytestreamHandler::pushMidiData(unsigned int const*, unsigned int const*, double)::'lambda'(juce::universal_midi_packets::BytestreamMidiView const&)>(unsigned int const*, unsigned int const*, double, juce::universal_midi_packets::U32ToBytestreamHandler::pushMidiData(unsigned int const*, unsigned int const*, double)::'lambda'(juce::universal_midi_packets::BytestreamMidiView const&)&&)::'lambda'(juce::universal_midi_packets::View const&, double)>(unsigned int const*, unsigned int const*, double, juce::universal_midi_packets::U32ToBytestreamHandler::pushMidiData(unsigned int const*, unsigned int const*, double)::'lambda'(juce::universal_midi_packets::BytestreamMidiView const&)&&) juce_UMPDispatcher.h:52
juce::universal_midi_packets::ToBytestreamDispatcher::dispatch<…>(const unsigned int *, const unsigned int *, double, <lambda> &&) juce_UMPDispatcher.h:186
juce::universal_midi_packets::U32ToBytestreamHandler::pushMidiData(const unsigned int *, const unsigned int *, double) juce_UMPU32InputHandler.h:83
juce::CoreMidiHelpers::Receiver::dispatch(const MIDIEventList *, double) const juce_CoreMidi_mac.mm:645
juce::CoreMidiHelpers::Receiver::dispatch(const MIDIEventList *, double) const juce_CoreMidi_mac.mm:702
juce::CoreMidiHelpers::MidiPortAndCallback::handlePackets<…>(const MIDIEventList *) juce_CoreMidi_mac.mm:750
juce::CoreMidiHelpers::CreatorFunctions::newMidiInputProc(const MIDIEventList *, void *, void *) juce_CoreMidi_mac.mm:860
invocation function for block in juce::CoreMidiHelpers::CreatorFunctions<(juce::CoreMidiHelpers::ImplementationStrategy)0>::createInputPort(juce::universal_midi_packets::PacketProtocol, unsigned int, __CFString const*, void*, unsigned int*) juce_CoreMidi_mac.mm:815
MIDI::MIDI_1UP_Deliverer::operator()(const MIDI::EventList *) 0x00000001c1a269b0
MIDIProcess::MIDIInPortThread::Run() 0x00000001c1a41e14
CADeprecated::XThread::RunHelper(void *) 0x00000001c1a292e4
CADeprecated::CAPThread::Entry(CADeprecated::CAPThread *) 0x00000001c1a2a610
_pthread_start 0x00000001a955ffa8