Im on Vodafone as well. I don't know how long you have been finding this but I found something similar where I go to work sometimes. Used to be fine on 4g, then went crap despite showing 4g. A few months later I went back and had been upgraded to very fast 5g. I noticed similar at one stage when things went from 3g to 4g. Not necessarily in the same area but in general. Maybe an upgrade is occurring in your area.
Don't know, used to be awesome, indoors everywhere.
Since 3g has gone off, it's rubbish.
It's ok early hours of the day, so I recon by later on it's just getting overloaded. It'll say 4g, but do nothing, then it will, then it won't. Like it's buffering.
I have a 1p mobile some now, so will test this out.
If Vodafone chucked up some 5g, I guess that would distribute connections and help, but no idea when that will happen.