I've had exactly the same problem with my HTC One and I'm on EE UK as well. My phone originates from Carphone Warehouse so it doesn't have any of the silly apps the networks put on the locked devices they provide so I'm pretty sure it's not a result of one of those. However, I can't be certain either whether it's faulty phone or network related at this point. I haven't changed anything on my phone recently to have caused this so I'm tempted to go with network issues. Ever since they launched 4G, EE has been having all sorts of issues so I wouldn't be surprised if this is just an issue with the phone having difficulties retrieving generic information from the provider. Your trick with resetting the phone worked on mine and it hasn't re-appeared since. Haven't had any issues with my 4G connection though so not sure if it has affected anything else.
My devise isn't rooted either, just in case anyone is curious in regards to that. So not an issue arising from that.