I've had this issue for a while and seems to be that the MPPT 15/75 is not spending enough time at the Absorbtion State even though I've trying to set it for a longer period. The overnight discharge is about 16%. As you can see by the graph it is reset on the second Absorbtion state for the solar day on November 14.
On day 14th November the BMV 712 resets the SOC to 100% on the second Absorbtion state but does not on all other occasions the battery voltage reaches 28.4V.
My system is 24V and a 140AH Lithium-ion Phosphate battery. I've set up the BMV712 as per the manual
So it would seem to me the MPPT 15/75 Absortion state time is not matched with the BMV 712.
Some guidance in the various manuals for how to successfully achieve a better co-operation between the two devices would be appreciated.