I have the same issue. Or at least pretty similar.
I have the m20d and run 2 L3T mounted on speaker tripods, 2 L3S horizontally placed, and 3 L3M's for monitoring.
When I connect everything goes smooth for the first hour or so. Last Saturday I was engineering sound for a band on a wedding and while the band was playing at the Waltz everything was fine, then there was a break and all good.
But the issue came right after the band started to play again, the second part of the chain of speakers started to misbehave. The way I usually connect is LIne6 Link Output - L3T Input - L3T Out - L3S In and so forth. Until there my chain works flawlessly, the problem seems to be after I connect the secon poart of the chain... the next L3T and L3S and the 3 L3M's
After some period of time, the speakers begin to reconfigure themselves as I can see that happening at the L6 Link screen at the M20D, at first I thought it was a flaw from the mixer, and then the power consumption was just too much and the speakers weren't getting as much power as they need to. But Sincerely, I don't have a clue now as what to do.
Any thoughts? Will be really appreciated!