Another thing that might cause you problems.... Voice Mail. Apparently that doesn't work on WiFi Calling right now either (at least thru Verizon where I am). Because Voice Mail has become an app for some carriers and requires the voice mail be 'downloaded', WiFi calling can screw that up.

The problem I personally am running into - Since the last Android update: WiFi calling has been turned on in my phone and the option to turn it on & off has been removed (WTF!).
While on WiFi, I will get a notification saying I have a voice mail. But when I go to voice mail, it says it can not download it. I have to actually turn off my WiFi to connect back to 4GLTE, to hear my voice mail.
Again, this is with Verizon on an Android phone after the latest updates. And it is PISSING me off.

No settings in the router is going to fix the above problem either. This is one time the Apple fan boys can have a good laugh at us :(