I set the capacity to 280ah this morning at 100% charge. So that should be sorted now. I think my issue came from the fact I had to swap the BMS as the old one had a fault. When I did that I just swapped out without fully charging/discharging the cells first time round. So it probably messed up the internal settings.Yep, seems so. And the top balance seems pretty good. All cells were above 3.5V at a certain point in time and none was above 3.65V.
Now wait for full discharge (until the BMS disconnects) and share the BMS information for the battery capacity in Ah.
But in general - with 15.42kWh charged into the battery it looks like your cells are pretty OK for 280Ah cells. The one with the lowest voltage on the chart above is likely the one with the least capacity. It will dictate the battery Ah capacity.
Out of curiosity - what cells are you using and where did you get them from?