I'm on firmware 2.13.18, using a Pixel 6a.
After updating to the latest firmware a few weeks ago, I've been experiencing audio glitches quite often compared to when I got them new, which had no glitches whatsoever. One of the update was adding support for 24bit/96kHz aptX Adaptive, which in hindsight is probably the most obvious thing I should've tried investigating.
There is a toggle in the Sennheiser app that toggles High resolution audio mode. Turning that off does not fix the problem! Looking in the developer options, it's still using 24bit/48kHz aptxHD, and the glitches still happen. Turning off aptxHD in the Bluetooth options fixes the problem, but it will revert back to SBC and not stay at aptX, so it won't do either.
What you should do is go to Developer options in Settings, scroll down to Bluetooth Audio Codec and switch to aptX. It will now switch to 16bit/48kHz and the audio glitch should be resolved. Downside is that it seems you would have to go there and switch to aptX everytime you reconnect to your headphones.
My phone has no problem playing 24bit aptXHD audio using the BTR5, so the issue is most likely with the headphones itself.
TL;DR: I suspect the Momentum 4 couldn't handle 24bit audio, so switch to 16bit to avoid audio glitching.
I should've clarified, sorry!
Basically when it starts to glitch out, the audio stream would cut off for half a sec, then come back, then cut off, then come back, and so on. The phone would still stream the audio like it's nobody's business, video would continue playing without hitch, it's just the audio getting cut off and coming back.
Before finding the fix, I would have to turn it off and on again, and it usually fixes it, but then after some amount of time it comes back again. Tried factory resetting, but it's stuck on the new firmware so the issue still persists.