One other thing to check is that Pin #1 of the dimmer's DMX connector (the shield of the DMX cable) is NOT connected to earth/chassis ground in the dimmer packs. No continuity between Pin #1 and AC cable power ground with the power cord UNPLUGGED. This will cause very flakey things to happen... much like you are seeing.
Also check your DMX cable's connectors to make sure the shield is NOT connected to the shell of the connector, as is mistakenly done in some cheap DMX cables.Good luck!