It's not likely that your system is suddenly pulling that much power and the amperage reading is accurate - unless your system voltage is also sagging significantly during transmit - that's easy to verify. Much more likely that you're getting some stray RF into the EMS box that senses the shunt current. Some of the older EMS boxes were more sensitive to RF and it was a known problem back in the 2010's, I know there was a fix for it but you had to send the EMS box back to Dynon.
Short of that, if you have a break in the coax you can be leaking a lot of RF - this is not likely in the coax run itself if you are using RG400, but would probably be at the termination ends, either at the radio or the antenna. Check those ends, cut and recrimp if they are suspect.