@maxmp, I did some additional troubleshooting. In order to start with a clean slate, I unpaired all BT devices, exported Poweramp settings except presets, uninstalled Poweramp, reinstalled and imported settings, and recreated several presets.
It looks to me like there several things going on:
Poweramp is consistently confused by two of my Google Home devices. One is a Google Home and the other is a JBL Link 300, which is a Google Home-like device with better sound. Almost without exception, Poweramp loads the wrong preset for these devices. Neither closing the app nor disconnecting and reconnecting BT helps. Rebooting the phone doesn't help either.
For other devices, Poweramp sometimes selects a preset for the wrong device. Closing the app and restarting it seems to fix it.
Poweramp often shows a BT device twice with one of them selected in the preset list of devices connected in the EQ Save window (see screenshot).
Now that I have a better understanding of these issues, I can work around them most of the time, but I’d appreciate it if they could be addressed in future releases of Poweramp.