Magnum charging problem

Chesterboy

I have a Magnum MS4024PAE, solar panels, SunXtender AGM batteries, with grid to charge batteries. I prefer to set AC In Connect to VDC Connect, but charger won’t proceed past Bulk to Absorb when set that way. Very strange. It stays in Bulk for about 30 minutes and then stops charging and returns to Inverting. It does not behave this way when I set it to AC In-SOC Connect. (But I don’t trust SOC Connect, as it becomes less accurate over time. Last night the batteries went through the complete three stage charge and were at Float with zero amps in, but BMK meter said 95% SOC, when it should have said 100% SOC.) Any help would be greatly appreciated