When the connection goes down, are you able to access the Three website? Does the sim card work in other phones and does the phone work with sim cards from other networks?
Hi three_thoughts!
I did not check the three website. I can anyway exclude is a sim problem: here's the details of my experience.
I had an unlocked Lumia 920 with a three uk pay monthly plan that allows tethering. Tethering always worked on my phones. I upgraded to 8.1DP and the problem started to appear, making the cellphone almost useless (i use a lot of email whatsapp and skype, so not being able to get notifications because the data is down is hard to swallow).
I went to three to check if my sim was faulty (as they suggested), they even make me switch to a new sim card. This did not solve the problem so basically i traded in my upgraded 920 with a 8.0 unlocked lumia 925 from computer exchange which is working beatufully now.
That sim is working normally -tested a few minutes- with other phones in my house (lumia 610, lumia 630, lumia 720).
As i said above my grifriend just bought a new unlocked 630 from tesco (OT: a bargain!) with 8.1 preinstalled and she uses a pay as you go three uk sim card, so she should spot the problem, as the three pay as you go does not allow the tethering. She said that after a month o use she had a problem with data only two or three times. She is a heavy whatsapper, so she would have noticed the problem. I'd say twice in a month is a problem that can be occurred in any other ways (poor network, app crash, etc, so i would not count that in this investigation).
I just upgraded my bronek screen lumia 720 to 8.1 to check further with my simcard so we can have more details, BUT since the 630 which is only 3G is working i'd assume this is a problem between the lumia 920/925 (and probably 1020 and other 4G phones) 4G radio chipset and the three network, i am not sure i will be able to replicate it (the 720 istelf is 3G only).
Hope this can help someone who has better insights than me.