It happens with my with JBL E30 Synchros Headphones (wired). I've never used wireless headphones so I can't tell you if it happens with them as well. What is interesting it only happens with Bass Boost, not with the Sorround Sound and EQ presets (Flat, Normal, Club etc ) Spotify remeber my bass bosst level as long as the hedphones are connected. When I plug them out and plug in again (and also turn off spotify and turn on again) it resets. I would be grateful for any advice or help in this matter. If you need any further informations pls let me know :)
However.... That makes sense when I am switching between headphones and car bluetooth, as using equaliser + bass boost with my car audio just sounds bad. So when my phone resets the equalizer with car bluetooth radio connected it just sounds better (I can adjust audio settings on car audio).
But still, when I use headphones it is really annoying. And there is no easy way of accessing equalizer (some button on front pane maybe? many ppl asked for that).