Its been a while since I messed with a brushed ESC by Tekins.

Troubleshooting say LED's 1,3,&5, Voltage cut off low. If you're using nimh it would matter. Lipos Specs 2s or 3s lipos. Sure the FXR doesn't use 1s.

Setting you cut out Lipos 2s or 3s, 6v or 9v. You must be running 3s. For some reason it drop down from 3s to 2s, giving the error of LED 1,3,& 5 low cut off.

I don't know why it changed. Maybe when you disconnected the Lipo to recharge, Not turning it off disconnecting the ESC. Its all a phenomenon, electronics!! Or your brushed motor brushes are worn causing sparks and glitches.

Check you setting periodically, I do it with brushless. Upgrade to brushless, less maintenance, more quicker and power.

Reason why I asked you questions is to get a picture on what you have. Got away with brushed since Tekins came out with the R1 ESC 5 yrs +!!!! Been a while!!!