I had a WiFi connection stall even when the phone was connected to a charger when trying to set up strelaysrv for the first time (see https://forum.syncthing.net/t/errors-when-trying-to-run-strelaysrv-for-the-first-time/16818 for details). Disabling doze did nothing. The only reliable way proved to be using the Developer Options to keep screen on when charging.
Of course, my issues were under Android 7.x, so things might have changed in between, but my observations are that Android uses many different mechanisms to limit network activity when idle. In my case, it didn’t matter whether the phone was on battery or connected to a charger. What really mattered was whether the screen was on or off.