I am getting messages, just not the one I mentioned. Now that I think of it, I think that was Hangout message (meaning not SMS).
Hm... looking that up, I found another notice!
"Forward your text messages
Important: In light of spam causing potential issues with SMS forwarding, text message forwarding to linked numbers will end in July 2021."
That's interesting. When I first started using GV, I set it up to forward SMS to the linked number: that means sending the SMS to the native text app on the phone, as well as receiving it in the GV app. I turned that off shortly because of dual notifications, and having to visit both apps to clear the notifications.
I haven't had any problems with not receiving texts in the GV app-- but there is always the problem of 'how do you know you missed it, if you missed it'.
GV handling of MMS has improved quite a bit since I first used it.
I've seen other hangouts users commenting about a few things they thought hangouts handled much better than GV.
There are some things that don't work well with GV-- V-Card contact exchange is one of them. I don't know if that worked on Hangouts.