Inaccurate playback if started immediately after opening MuseScore

OS: Windows 10 (10.0), Arch.: x86_64, MuseScore version (64-bit): 3.6.2.548021803, revision: 3224f34

1. Open MuseScore by clicking on the attached test score - clarinet and piano
2. Click play button as soon as score is shown. If no response, click again until playback starts.
   Result:
   a) the piano sounds as if the sustain pedal is active,
   b) all the clarinet notes are played short.

Test score MSStartupTest.mscz

Recording of what is actually played MSStartupTest_recorded.mp3_.zip (renamed as zip to allow upload)
In this recording I managed to start playback approximately 12 seconds after clicking on the test score

I have monitored the CPU, memory use and IO activity as MuseScore starts when clicking on the test score. This shows that there is significant CPU activity and increasing memory use for approximately 12 seconds after MuseScore becomes active - i.e. 12 seconds after clicking on the test score. The attached graph has time divisions of 10 seconds per grid line on the X axis

If the score is exported to an mp3 the problem is not present.

mp3 export MSStartupTest_exported.mp3_.zip (renamed as zip to allow upload)

I can reproduce this every time, provided I can get playback to start soon enough.

If the problem is present and I delete the clarinet stave from the Edit Instruments dialogue, the problem is no longer evident but returns if I undo the removal. Similarly, if I remove the piano, the clarinet sounds normally but returns to short notes if I undo the removal.

Reported in the forum earlier here: https://musescore.org/en/node/315117 and here https://musescore.org/en/node/326232