Continuing the discussion from Plexamp Release Notes:
I’ve confirmed this issue affects (at least) v4.5.2 and v4.5.3. I haven’t had time to check for other affected versions.
At least in Cinnamon, Plexamp doesn’t seem to correctly notify or listen to the system player of track progress info. I haven’t pinned down the exact behavior - but attempting to scrub to a different timestamp in the track via the system track player results in the reported progress being reset to 0. Several other actions seem to affect this as well.