Hi, having some issues with BLE on iOS and wondering if anyone else is having any?

I’m using a Yamaha UD-BT01 and connecting from a late edition iPad.

The demo MIDI app works fine and so does my code - I can send and receive data from the target synth all well and good.

Problems happen when I start sending sysex.
After sending sysex, the UD-BT01 no longer responds to incoming data (from the iPad) and after about 10s it resets and the connection is dropped.

This process is repeatable. However, the same code running from Mac through to the UD-BT01 has no issues, so seems to point to iOS.

Anyone else had any issues? thx

Update: This works fine on Android and on 2 of my iOS devices but not the 3rd so looks like it’s an issue with that device rather than iOS.