In the victron connect app setting for absorption voltage is 28.8V (24V Battery).
But the MPPT never reaches this value but goes into absorption phase at 28.2V 
Any ideas, why this might be the case and how to adjust or correct it?
Thanks, Regina
Is the 28.2V when absorption ends the voltage at the battery or the voltage at the MPPT. Often if you have poor wiring, loose connections, poor isolators or fuses, wiring too long or thin then the MPPT voltage can be higher than the battery voltage dud to resistance. If this is the case use a multimeter to find where the voltage drop is occuring and rectify it.
Do you have a lithium battery connected to a GX device and the MPPT managing charging.
Its a system with AGM Deep Cycle batteries.Voltage is shown at beginning and end of absorption phase.
Are you currently somewhere hot above 25degC.
The AGM charging voltage is adjusted based on the MPPT temperature at the start of the charge cycle. If the temperature is above 25degC then the charge voltage is reduced. If it is below 25degC then the charge voltage is increased.
AGM batteries require this temperature compensation of voltage to avoid over charging when hot.
Thanks. MPPT has 33°C on the surface. This would explain 8 x 3x32.4mv = 259mV. This does not explain fully the difference between 28.8 and 28.2V as
currently experienced.
From device to device, there are calibration variances.
Victron will say that, bar the temperature compensation, a 350mv (1.2% at 28V) difference is acceptable.
I also have such differences between the voltage shown and voltage at terminals.
But I set the values in that way that at terminals to be what I want. (Measured with a trusted voltmeter).