I remember that you have to change sim 1 to 2g and sim 2 to 4g because you can only allow to set one for 3g. Used dual sim in the past, but not with meizu phones. In the settings there should be a SIMs and networks tab, (reference from flyme 5). Have you tried using only one sim on SIM1, might be hardware problem.
Thanks for your response!
I have only one SIM right now connected to SIM2, I tried connecting it to SIM1 but it won’t discover it from SIM1 socket. It’s like stuck on 2G only since it’s on SIM2.
I would be happy to hear if there’s a way to change that setting or override it somehow.