600ex-rt not linking or dropping link

[MDI]

I have three of the 600 EX Dash RT speedlites that are not linking or staying linked, if I do indeed get them linked for a hot minute. I cannot put them all in the manual mode. Out of the two slaves one stays ETTL versus M. Also, if I am fortunate enough for the speedlites to link, after changing the amount of light on the master it drops the sync and only my on-camera flash will work. I have to shoot a bar mitzvah next week and I need this to really come together. Thanks in advance  

[p4pictures · Accepted solution]

My standard way of working with the Canon radio flash system is to choose settings that are not close to the defaults. I know and have seen instabilities when lots of units are in a similar area and using the default settings.

Set the channel to one of the numbered channels - do not use AUTO and make sure all the units have the same channel set on them.

Set the ID to something far away from the default 0000. Personally I use a number in the range of 5000 to 5700 and make sure I have no repeated digits so something like 5136 would make sense. Again set this in each master and slave unit. 

Switch on the master first, then switch on one of the slaves and check for the link light on both. Switch on the second slave and again check for the link light. Make sure the slaves are assigned the correct group letter, even if both are in the same group. The master flash on the camera will be part of Group A - this cannot be changed - so if you want to have the same power output from the slaves then set them to Group A too. 

On the master set the mode from ETTL to M, the slave unit will not instantly switch to M only after you press the test fire button on the master or take a photo. 

I am not denying the reports of dropped links, but I have only seen this happen a few times with my own Speedlites. These have been with early units when there could be some unreliability when you use more than 6 or 7 units. I mostly found that on Speedlite workshops I used to run. Also I'm located in the UK, so maybe there is some difference in the use of the frequencies compared to USA and that might be part of the reason for the dropped links that people see. 

[MDI]

Thank you. You are very kind. I was told it was the 5G network off-setting things. I will try your suggestion. It seems sound and I might have better “luck” with your approach. I appreciate your time. Thank you again!