Hi Andy, thank you for the video it can’t be clearer to understand.
It’s not normal, maybe you can check your DMX monitor view in photon (touch left bottom corner of the app) to check if the signal then is correct. If there is no discontinuity in the DMX signal on your big fixture channel that could explain flashes.
It could also be the way you configure. photon. In the settings is it Multicast mode or Unicast (with the explicit artnet mode IP set). Unicast is better.
Sometimes it can also be due to a DMX issue. Sometimes you have to put a DMX plug at the output of the last fixture.
I hope it could help you