Juce 5.4.4 has introduced a check for duplicate parameters:
AudioProcessor::triggerDuplicateParamIDCheck()
The check is deferred with an AsyncUpdater. There seems to be a bug, as the duplicateParamIDCheck object is recreated for each parameter, thereby flooding the queue. If the queue is full (many parameters) PostMessage fails subsequently (didn’t try on macOS yet), causing problems for the UI initialization (timers wouldn’t start).
JUCE team, could you please fix that?
I think its nothing more that adding && duplicateParamIDCheck != nullptr in the condition at juce_AudioProcessor.cpp:460.