You might have a 55 amper, not a 60. There were a few instances of the factory putting on the wrong label for amps "size" a while ago.
Very hard to tell unless you are for sure at a low enough SOC to see the 60 or whatever it is supposed to be. With an Li at 27% and #4 wire, there is no way you won't see 60 or a bit more amps.
ISTR you said you have two 60 ampers? Try it with the other one and see if it does all 60.
No big deal if it is a 55 instead of a 60 for what you are using it for. Another way to confirm the converter max amps is to run a big inverter load off the battery and then start the converter( from a different 120v, not from the inverter!, so no loop). Say the MW pulls 125 amps and with the converter on, the monitor shows minus 65 amps--so it is a 60. If amps are -70 it is a 55 amper.