Measure the cells directly with a multimeter - how does that compare to the bms values? (I bet the cells are just fine).
You need to isolate the problems, and think through them logically. (Very hard to do on your own battery- that’s why we are here to help).
My guess… if you add up cells three and four on the bms - they total about what two cells should be. So I think your #3 or #4 lead is loose (either on the battery or wire loom or bms).
After verifying your cells are ok, maybe completely disconnect to bms and then reattach. Looking very carefully at the leads for #3 & #4. (Especially anything you did - crimps, etc).
If it continues try the wiggle test - while running and looking at the display- wiggle one wire (a little) to see if you have a bad connection there. Check all connections.
My guess is you have a bad connection somewhere… there is also a chance you have a bad bms. The challenge is figuring out the problem.
