Some thoughts.

1) You've been told to take a close look at battery posts/terminals. Do that.
WHile at it, do either James' mod or my mod in this thread here:
https://www.crossfireforum.org/forum...le-engine.html

2) I still think it could be the battery.

3) There are several RCM failure modes. Solder is only one. The relays can be intermittent. Consider buying a new one and sending yours off to be reworked by DJ -we all need a spare!