That is a common problem with off brand stuff. The DMX drives in them don't play well with others/cut the DMX signal down. Some Chauvet stuff has this problem as well and wants to be first or last in the DMX chain to play with others.
With that many fixtures, I would recommend getting a DMX Splitter. It would help boost the DMX signal and you can put problem fixtures on their own line so they don't effect other fixtures. Elation makes two, the DMX Branch 4 and the Opto Branch 4. They are the same unit, just one is a single space rack mount unit and the other is a stand alone but comes with rack ears. It takes two spaces in a rack however.