What you haven't documented yet is what your solar input is? How many panels/watts are you feeding into the controller? Also, how exactly are you measuring the state of charge? By voltage?
If you have an inverter connected to the system, there is power draw from the inverter even if there is no AC power being produced. Depending on the size of the inverter, you might be consuming 500-1000Wh of power just leaving the inverter turned on.
Let's say your inverter consumption is 500Wh per day, and you only have two 100W panels charging the batteries. The two panels might not be able to replace the amount of power the inverter draws in less than ideal conditions.
Do those batteries have snap-caps? You get a far more accurate reading of the state of charge using a battery hydrometer rather than reading the voltage.
What's the voltage and amperage ratings of your panels? You have them wired in series? With an MPPT controller, you'd need >36V or so to properly charge a 24V battery. The battery will want to charge at up to ~29.6V, and the MPPT controller needs several volts of headroom to function properly. It will be helpful to also know the charging parameters that are set in your controller?
A better pic of your battery setup that shows the positive and negative connections clearly will be more helpful.
Until we troubleshoot what's going on, the first thing I would recommend is to turn off the inverter, to at least eliminate the constant parasitic draw.