FP2 Android 9 Dual SIM change networks (2G/3G/4G) not possible any more

Dear community,
I recently updated from Android 7 to Android 9. Everything went fine - almost everything: I discovered that I cannot switch the SIM cards between 2G and 4G any more.
My usual setting (as it was also during the update) is the following: SIM1 is registered to 4G, SIM2 is registered to 2G network. As only one SIM can be registered to 3G/4G at the same time, what I did when I wanted to have 4G on SIM2 was the following: choose 2G for SIM1, then choose 4G for SIM2.
But since Android 9, when I choose 2G for SIM1 nothing happens. For SIM2 the selection menu remains grey. The connectivity of SIM1 gets lost as before, but it does not register to 2G. Furthermore, when I re-enter the menu for SIM1, it is again on 4G. So, my interpretation is that the new setting 2G is not saved, so that the 4G piece of hardware is not made free to be used for SIM2. All that came into my mind, was several reboots of the whole phone, but this did not help.
Does anybody have the same experience or an idea what to do?
Thanks for your help and best regards

It would be interesting to know what happens if you swap the SIM cards.

Good idea, I just tried. The network status stays with the SIM card, and the behaviour of the phone stays the same.
Initially: slot SIM 1 = Swisscom = 4G; slot SIM 2 = blau = 2G
now: slot SIM 1 = blau = 2G; slot SIM 2 = Swisscom = 4G
And when I switch Swisscom from 4G to 2G, this switch is not executed.

Have a read abloesung 2G at Swisscom.
Perhaps this is the cause.

I am aware about this. And that’s the reason why I have to switch all the time the networks because the 2G network in Switzerland is dying, and if I want to use the second SIM card, I have to bring it out of 2G. I did this switch regularly before the Android update. And the Swisscom SIM always accepted 2G (with the consequence that the coverage was much worse, especially in my house). But I could always do that switch to 2G. Now I cannot do this switch anymore. Perhaps Swisscom has changed something behind, but it would be a big coincidence, that they did so exactly the night between 5 and 6 May when I updated to Android 9.
I tried something else: only the blau SIM card in slot 1. It started in 2G and the menu was grey. Then I got asked "you use blau as the only SIM card. Do you want to use it for calls, SMS, and data? I accepted. Then it was in 4G. But like before, when I switch to 2G, this switch is not executed. After entering the menu again, it says 4G. By the way, the switch from 4G to 3G is executed. After entering the menu, is says 3G. When I switch from 3G to 2G, after entering the menu is says 4G again. Strange. So I believe, it’s a software issue.
Now, if I cannot switch anymore the networks, but have to take out the Swisscom SIM, to be able use the blau SIM in 3G/4G, then it becomes really annoying.
I am hoping for a different solution.

got it!
I have to switch “mobile data” from SIM1 to SIM2, that it performs the switch from 2G to 4G in a way, that the SIM card with mobile data registers to 4G. That’s a solution. Actually even more clever then before. But you have to know it. Thanks for making me try…


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