Manually selected mobile network changes when signal strength drops Although this might seem quite unusual, it is essential for me. I live in a border area and I have two sim cards in my phone (however, I think this problem also affects single sim devices):


SIM 1 is from a French operator
SIM 2 is from a Swiss operator
The SIMs should be connected only to their home countries and should be unavailable if the network of the operator is unreachable


So if I am in Switzerland, only SIM 2 is active, if I am in France, only SIM 1 is active - and if both operators are available (= I am near the border, 80% of my life) both are operating. 

I have an ASUS Zenfone 2 Laser ZE500KL, stock Android 6 without rooting (and I would like to keep it that way if possible). The behaviour described above is the default thing what happens on a Windows Phone and that's why it really grinds my gears why Android tries to be so creative. Basically this happens:


selecting the network provider manually is OK
however, signal is lost sometimes (e.g., in the garage) so the Swiss card starts roaming in a random French operator's network
the phone only switches back to the Swiss operator if the "random French operator's" network is unreachable (or if I do it manually)


I know that this is an edge case, but it is really essential to me. Unfortunately, I did not have the opportunity to try it on other Android phones (according my colleague he has the same problem, with a Samsung "god knows which mid-range model with Android 4.4"). 

I am looking for a solution/workaround which does not involve regularly pressing a setting or changing sims and preferably does not need rooting. APN Lock for me did not work.
It seams to me a problem of Android 6.

I have a similar problem with SONY XPERIA XA.

my behaviour:

SIM1: Manual on Sunrise (CH)
SIM2: Manual on TIM (I)

Reboot the phone:
SIM1: Manual on Sunrise (CH)
SIM2: Automatic (it select the power operator May Swisscom, TIM or Orange).

So afer any reboot you should select manualy the network (if available!).

Don't know how to create a BUG request for android.

I allredy tyied to contact SONY, but no way!

regards
Stefano