Imo
Charge controllers and Buck devices are not going to work, they only allow current flow One Way
The $&_:; Xantrex is a combo unit inverter/charger
And must have current flow into the inverter when not charging
If theses were discrete separate devices, a charge controller would be a good choice for regulating converter voltage
A resistor is not going to work either
Because it will be inline the current path when using inverter power, thereby reducing the input voltage for inverter use
The basis of these problems is the Tesla battery is Not A 24v battery, it's a 21v battery that charges with 25v,
Most DIY RV installs are using Victron Multiplus inverter/chargers
Depending on monies available, I would dump the Xantrex and go with separate charger and inverter
And install an mppt controller between charger and Tesla battery, also add the contactor on the charger input 110v , just in case the charge controller failed
Separate units while taking up more space, are usually less expensive per pair than the combo units
And if one fails are cheaper to replace or repair and also less inconvenient
