It appears from your description that one of the midbass drivers is out. There is an internal passive crossover so one of the positive or negative wires could have come off either the crossover board or the midbass driver terminals. Simply pull the four outer screws, remove the speaker and grill and check the internal connections. There are four more connections between the crossover and tweeter that shouldn't interest you. While the polarity of all this is marked on both the speakers and crossover, please be cautious and take note of everything.
Manually see if the midbass driver is frozen so that it will not move. If that is the case it has been permanently damaged from heat (by too much power). If that is the case you will also notice a distinct burnt smell when you remove the speaker from the pod.
If you have a multimeter you can check continuity across the midbass driver terminals. You should get a DC resistance reading of between 3 to 4 ohms. If it reads 'open' then this is another indication of damage. If you don't have a multimeter then you can check the midbass driver by circumventing the passive crossover and jumpering the crossover input directly to the midbass driver. DO NOT try this technique on the tweeter. This will also eliminate or confirm the passive crossover has an issue.
You can also switch the left and right drivers while leaving the crosovers in place to isolate either the midbass driver or crossover.
Bullet has discontinued the HollowPoint 650 HLCD some time ago so replacements may not be available. If it comes to needing a replacement midbass driver only I may know where to find one among the dealer network.
Let us know how it goes.