I was having problems with an errant battery and the new firmware seems to be what was needed.
What I didn’t know was you can only apply it to one battery at a time, and when you have 6 B300s batteries with 6 huge cables to wrestle with, well…I now need a nap 
At least the update worked as that would have been exasperating.
Follow up. The update worked for one day, but the next day the one problem battery started misbehaving again.
The problem was that it would stop recharging before getting to 100%; it would then go into STANDBY mode at around 79% while the other 5 batteries would be at 100%.
Looks like Bluetti is going to replace it, thank goodness.