If you're still having issues I'd head to the victron forums - not only are they far more experienced (you having this on a boat is irrelevant, half the people here didn't even even understand you have lithium batteries!), but this isnt actually a "boat" issue in so much as a solar/gear issue!
I'm not tracking well ad I'm super beat but I'd start at unplugging everything and just watching how your mppt is acting with sun to your batteries for a day (am i correct in that you have two? Check they are set up exactly the same you can copy the settings across if you link it all which you should do anyway too).
That is either the problem or absolutely not it, and those parts are all good. Thats important to isolate!
Unplug everything else and just run those 3 (and the BMV which you really ought to have in this setup if you dont).
Add in the multiplex next and see what happens. Then add loads one at a time. Take notes and readings.
Lastly any converters.
Offhand if it's not a bad mppt setting I'd say you got a bad Dakota. The loads and what they are are mostly irrelevant, you got a bad Dakota or board in it, or.one part of your setup needs serious attention.
