Help me diagnose JBL audio issue (bass cuts in and out)

Hello,

I have a 2011 Prius with JBL audio.

A few weeks ago i seemingly blew my left rear door speaker. What happened was, while I was driving and listening to music, the bass got much quieter. It isn't gone completely but the frequency response seems very inconsistent compared to how it was before, like the low end is mostly cut out.

After troubleshooting with the touchscreen sound controls, i found that the left rear door speaker was definitely the issue. Sounds blown. BUT I am confused because over the time that it has been broken, there have been a couple instances where I'm driving and listening to music and the bass will randomly (but temporarily) come back in full. This makes me think that it could be a loose connection or an issue with the HU or amplifier.

So my question is: is this just a blown speaker? Or could it be something else? I don't want to replace the speaker if that isn't actually the issue. Thanks!