Pylontech US 3000 One of 2 not charging fully

Welcome Hein.

Looks like the batt needs some TLC, the cells in that bank are out of balance.

Best case you learn to get them back in line.
Worst case, warranty replacement.

Have a look here: (ignore “Victron”, focus on what their batts are doing and how it was handled.)

And here:

And here: (for the firmware if you want)