I had a similar problem using Cashu.me (desktop browser) a couple days ago... though, it almost seemed like the problem was with the nostr:npub1kvaln6tm0re4d99q9e4ma788wpvnw0jzkz595cljtfgwhldd75xsj9tkzv mint wasn't responding or something.  Regardless, the tokens seemed to be marked as both spent and pending within Cashu.me; and it wouldn't allow any transactions after that.  I ended up Exporting Active Proofs and Reset the wallet, and all is well now; but, I feel like I should let someone know.

If this is the wrong place to let someone know, sorry for the longish explanation.  Cashu.me doesn't seem to have a Nostr profile that I could find - which would be great for reporting bugs.