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).
But then pushed back to 10 years after the heat death of the universe.