question

Hi Sy. Your Smart mppt won't leave Bulk until it reaches it's target Absorb/Float, which might be 14.4V (say). If this is happening daily, it suggests an imbalance in system design, too much load, or suchlike. Or a fault - heaven forbid.

But you'll need to provide more detail of your system for any useful answer. Please describe it as best you can, and there's plenty of helpers here who'll assist.

12.8 for 12 volt battery is not "at 100%charge"

Voltage can say bugger all about SoC. You need to understand the actual state of charge of the batteries.