audio drops after changing 4k timeline preference to 1080 for viewing

6 may 2022 today i have opened up premiere to start a new project (no changes at all on my system) created a new project, imported 4k (4480x3096) footage at 25fps (which has guide audio) and seperate 48K 24bit wav files, (nothing unusual) timecode on pics and wavs match so pull all vision media into a native timeline and then sync each audio wav to pics. timeline plays pics and sound no problem in my imac and through my external speaker system. Then as I always do, I change this sync timeline to a 1920 x 1080 so that i can preview also through my 3rd external sony standard def monitor. Have never had a problem with doing this.

But today when i then hit play the audio drops out.  I can see meters moving and you can still see waveform present on clips in timeline. I then turned the timeline back to the native 4480x3096 and then hear the audio again.  I tried creating brand new project. tried new sequences from fresh (so not creting from a clip selection) still no good.   I feel a bug has appeared. Any ideas out there?