I’ve bought a Fairphone 2 something like three weeks ago and I am using Android 6. I made the purchase to the French operator Orange, as I have a phone number from them. Since I live between Luxembourg and France, I also have a Luxembourgish line at Orange LU - hence I first found the double SIM system very attractive.
I started using my Fairphone in France, having the French SIM card in slot 1 and the Luxembourgish one in slot 2. Everything worked fine during my stay in France, although I paid no attention at all about this (seemingly usual) issue regarding 4G that can be configured on only one SIM card. Arriving in Luxembourg, I tried to reconfigure the system so as to fetch data from the Luxembourgish line (although roaming is now free within the EU). I then came across the caveat regarding configuring 4G, but I followed the instructions and set 2G on SIM1 and 4G on SIM2. I also tried enabling/disabling data on SIM1, using the different settings (settings/SIM cards and settings/data usage) that are available.
Nevertheless it turns out that I cannot maintain my connection to Luxembourgish data at most 24 hours in a row; then I lose the connection and have to reboot the phone in order to recover data access (not to mention sometimes where I am just stuck and have to try any sort of ‘magic’ enabling/disabling the SIM cards). Finally the workaround: I am on roaming with my French SIM card and everything is stable since 4 days. I cannot possibly understand why, since by default Orange FR uses Orange LU channel (and then I assume the infrastructure my phone uses to communicate is the same than with my SIM 2).
So one possibility is: although I disable data for SIM 1, the way the Fairphone is handling data with SIM 2 may be somehow different - and then leads to crash at some point. One way to check would be to switch my SIM cards, but before going further in the experimentation, I’d like to ask: has anyone experienced the same issue with data in 4G set on SIM 2, while roaming on SIM1?
Also, I found some posts mentioning data crashes in the forum, but they were quite old (early 2016) and not conclusive, so this is why I open a new post. Apologies if this question has already been addressed before.