I don’t know if you’ve already tried this, but I’ve had weird behavior with older Pi3s when the power supplies weren’t up to snuff.

A good 5V/10A (yeah I know they only need 5A) sorted out one of mine that had a heavy load of Neopixels running on it, even though the neopixels had their own 5V supply.

I haven’t needed to get a Pi5 for any of my projects and really use them as big arduinos in certain uses (better for camera detection and remote reprogramming).