from this post:
The charge controller isn’t allowing any further amps into the batteries.
It’s happening, but the controller isn’t doing it. The batteries aren’t allowing any further amps into the batteries.
The mppt controller reacts to decreased current acceptance by moving Vpanel toward Voc; in the first display we can see Vpanel as 39.8v.
When the system is loaded (second pic) the MPPT algo has picked one of at least two points at which it could get 5.6A at 13.2v for the battery. We know it can’t be Vmp or the panels would put out too much.
This pp happened to be below Vmp, at 17.3v. One would presume another one would be above Vmp somewhere.