Were you able to solve this already or is the problem still there?
As far as I can tell that setting only applies to the Magisk app (it’s in the App section), not system-wide.
Since this involves mobile connectivity, have you tried resetting your APN(s) to default?
Settings → Network and Internet → SIMs → [Name of provider] → Access point names → ︙ → Reset to default (Might be slightly different under stock FPOS)
Probably unrelated, but always a great start 
Also have a look at what’s set for Settings → Network and Internet → Private DNS
Oh, your provider is Vodafone 
Well, there have been a lot of problems with them in the past, for example with the previous update…