Error
Cause
Base on the error message of "System.MissingMethodException", I figured there was some sort of mismatch going on. I checked the files and noticed the dates are off and these are typically the same. They're not always the same, but taking into consideration the error message stating a method is missing.
Since I was suspicious about the mismatch, I checked the rma_install.log to see if there was any issues and I see that it was skipped:
A skip could happened due to MangoMonitor not shutting down fast enough, permissions, etc.. They appear to be running via network shares, which we originally had issues with. They also appear to have a very old version of MangoMonitor, which could have attributed to the issue as we haven't made a change in MangoMonitor is a very long time so there shouldn't be a missing method unless it's old.
Resolution
Update Route Manager, and ensure there are not any errors which occur.