I suddenly have the same problem a couple others have mentioned. I use an ST-E3-RT to link three 600EX-RT flashes with a 5D MIII. Recently the link started randomly dropping on all the flashes (after some random amount of time from 1.5 minutes to about 4.5 minutes). The only way to fix it is to turn everything off and reset each flash to slave. Not good during a photo portrait session since it happens multiple times.
I have tried a ton of troubleshooting. I used to shoot weddings so I have 2 cameras and two transmitters. I've tried all combinations and the link drops regardless of the camera or transmitter and even if the transmitter isn't on a camera (hand held for test). Both transmitters drop. I tried several different channels and auto - no change. I tried each flash by itself to see if is something with 3 flashes - no. Same problem with only one. I have 4 flashes and I tried the 4th just to see - same problem.
One last piece of info. When the link on the flash drops, the light on the transmitter still shows green (so it thinks it is linked). Turning on and off the transmitter doesn't re-sync the flashes.
This seems crazy. It can't be the camera (I even tried it with a new R6 that my husband got - same issue), because it happens when not connected to the camera. Why would both transmitters go bad? Why would all 4 flashes go bad. I don't know what else to try.
Any ideas, I'm pretty desperate at this point.
