It seems to be the way it should be: GSM/WCDMA/LTE Auto. I was in France a week ago and it had serious issues roaming and data roaming, i had to change it to GSM/WCDMA auto or WCDMA only to make it work. and now back in UK, i set it to the same setting it used to be before I left.
On a side note, I have realised that EE is having data network issues in my area. I tried the SIM in another Galaxy S3 and it had difficulties loading websites, but, it COULD make calls without problems.
Also, no crashes as of today on the One, I still can't connect to my 2.4Ghz wifi router. Could the fact that I was using 5Ghz somehow messed something up inside the One?