Voltage disparities in MS4048 with ME-ARC 50 vs Tristar and multi-meter

Hello All,

Thanks for taking a look at my question and throwing out ideas and thoughts.

I have an issue that I think has been there since the time of install.

My Magnum Dimensions MS4048 inverter/charger seems to have always been under-reporting the voltage.  When I first installed back in 2018 it did not seem like much of a difference.  Now that my batteries are getting older I've been noticing that it is affecting, first my LBCO (low battery cut of for the inverter) and now my charging from generator.

Picture attached shows the disparity between the different readings as well as a bit of the wiring set-up.  I thought the BMK (battery monitoring kit may be the issue but when I disconnect it, the voltage does not correct.  (Tri-star voltage shows 54.2, it's a little hard to read)

The voltage at the terminals on the inverter are the same as the multimeter shows for the connections for the battery in the combiner box 53.7 volts.

I have not received a call or reply to my requests for assistance from Magnum (it's only been a week.)

I have double checked the connection between the inverter and the ARC and they appear to be correct according to the wiring diagram in the install manual (I did trim the cord and replace the connector). (pictures also included)

Any thoughts on trouble shooting this issue? 

Thank you for your help

Off Grid - Magnum MS4048 Inverter Charger with ME-ARC and ME-BMK, TriStar-MPPT-60 Solar Charge controller with Morningstar remote digital meter,  Tri Metric 2030, 500 amp/50mv shunt  4-Canadian Solar CS6K-305MS 60 cell monocrystalline panels. 305 Watts, 48Volt battery bank with 8 Crown CR430 (430 AH)