Constant Errors

It's been most likely triggered by an ingame-action, unrelated to the build.

The underlying problem is presumably Cauldron's tile entity placement simulation, which leaks some state and doesn't clean up properly by at least calling invalidate on the tile entity.

You could investigate changing the log4j configuration in the cauldron jar (log4j2.xml) to filter the warnings, but IC2 already throttles them heavily. The only "damage" is that the affected block may be unable to send/receive energy and your logfile grows somewhat. It's not CPU intense.