I'm have Arrow OS with Gapps, rooted and NL KPN Network as well.Could you check the settings under Network and Internet > Mobile Network and tell me which Preferred network type, system select, cdma subscription you are using?
Otherwise i have no clue why this doesn't work for me. My guess is the OS doesn't work well with my provider (KPN) but why i have no idea.
All i can say is that i can reliably replicate the problem by enabling VoLTE/VoWifi. The moment that is turned on, any incoming calls are Unkown.
I am using the default phone app btw.
I had to adjust the modem settings to get caller ID working. See my other post Link
When updating the firmware you need to redo this.
Didn't had to changed anything under Network and Internet > Mobile Network