Under discharge 1 cell went low

What could be the reason?

Could it be the point in the battery string to which i connected the inverter? Maybe its better to connect it to the middle of the battery bank?

I will try to attach pictures

We will need a lot more information to help with that question, but 1 cell going low usually means you have 1 weak cell.

To post pictures keep the file size of the picture under 512k so you can post it.