Flamma FX11 - bass signal got weak all of a sudden?

I use my FX11 for practice quite a bit. A couple days ago, I fired it up and found that I couldn't get enough volume out of the bass to keep up with the bluetooth input from my tablet (backing tracks). It's driving me nuts. It doesn't seem like a problem with the device's output since I can still crank up the bluetooth input as loud as I want. Has anyone else experienced this?

Things I've tried:

• Charging the device to 100%
• Changing out my bass pickup batteries
• Different headphones
• Messing with the different amp/effect settings