[flashing grey screen]

 unless you try the sync cable I'm not sure you can rule that out as a possibility. I've started using my cable as my lights are very close to being in the way, but not quite, and also I'm stuck on a main road with many vibrations, and this has helped reduce/clear any grey screen sync issues I was having

[flashing grey screen]

The room lights are directly between the base stations so could quite easily be causing sync issues from interupted line of sight? Especially if the lights are on. Try using the sync cable?