Refresh rate slowing down after using proximity sensor

If I activate the proximity sensor during a phone call, when the display turns on again the refresh rate noticeably slows down, even below 60 Hz. It also happens when listening to voice messages (both in Whatsapp and Telegram, didn’t try other apps). It’s quite annoying.
Fortunately it goes back to normal after locking and unlocking my Fp5.
I also noticed that this happens only if refresh rate is set to 90Hz, no problems at 60.

Here is a slow motion video I recorded to show the problem:

Is anyone experiencing the same thing?

Not sure if I’m having the same issue here, but I too have noticed the refresh rate buckling randomly. Though it mostly happened in the first week of me using the FP5, then I haven’t experienced it since.
Nor did I ever narrow down what caused it. And I would describe is as more like erratic frame pacing. Because it’s very irregular and choppy.

Hello,

I have also noticed that the refresh rate changes randomly sometimes even if it’s set to 90hz. Turning the screen off and on seems to fix it.

It doesn’t happen very often, but when it does it feels slower than even 60hz. It’s a weird feeling.

Thank you Spike and @Nabalazs for your feedback. My problem though is very specific. Is anyone able to replicate it?
I’m wondering if it’s happening only on my Fp5 or not.