With the ACR in there, it's logic is "Is there charging voltage available?" If YES, then connect the two systems. Your solar panel and MPPT are putting out 14.84V. That will flow into the batteries for sure, and if the LiFePo4 battery is fully charged, then the current will flow into the truck battery.
This is one of the reasons I like the manual switch on my ML-ACR 7622. To disconnect if I want to.
Also, you could lower the "charged" and "float" voltages in you MPPT settings, that would reduce this effect, but not eliminate it.
Also, I think you don't have a Victron BMV, do you? With that you could at least confirm the LiFePo4 house battery's SOC and see any current flow.