When I was a young lad, it was standard practice for many internet apps to work on the principle of local caching. You'd connect to the internet, refresh your local copy, disconnect, and then work from the local copy. NNTP worked this way, POP3 worked this way. There were even apps that grabbed the current news and stock prices in the brief minutes that you were connected.

It's a good model, and it would work well here, and for any circumstance when your connectivity is intermittent.

Integrate it into KeePass or 1Password. I'm sure Yahoo will pay a billi for that.

I once had a similar issue with a hotspot, that required email confirmation but didn't let me access my email.

It's possible to work around when you have a phone connection with limited bandwidth and a low monthly cap, but meh.