Dual SIM card problem

[Fmaks]

I have two sim cards from different providers. Each one is working perfectly if used alone. But when I input both my phone (Z3 dual sim, Android 6.01) recognizes only one sim card and doesnt "see" another. It doesnt make difference which slots I use it is always the same.

I tried restarting phone several times and did network reset. Nothing helps

[Gustav1]

I have been using Z3 dual D6633 for a long time with two sim from different operators and countries. No problem (except weak connection).