I've just run into an issue that I've never encountered before, thought I'd post here for anyone thinking of going digital wireless. I just did a couple of weeks touring out in Germany, flew over with my Kemper and my old Line 6 G90* which I've owned and gigged for about 10 years with no major issues.
Rehearsals all went fine, come the first show we soundchecked on new batteries and everything was great. Get onstage and my signal starts getting undergained and cutting out, eventually the tech swapped me onto a cable. On the next show, I changed over to my other pack with a brand new patch lead, brand new batteries again, same story that everything is fine in soundcheck but, come line check, the tech starts getting the same issue.
The conclusion we had to draw was that in a room full of cell phones all pointed at the stage, 2.4ghz wireless systems don't behave well. I switched over to a traditional UHF system which a member of the crew managed to 'borrow' from another act who were currently off the road and, hey presto, no more problems.
* If you have to fly with a rack, the Gator 4U Short rack is exactly the max dimensions to fit in an overheard locker, so you can carry it as hand luggage. Spent ages trawling through rack cases to find this out.