I assume it's timing out without amber ever seeing the request. If it's using the applesauce-accounts package one top of the signer there is default queing for requests. So it could be that it's waiting for the last request to be accepted or rejected before sending the decryption request

Maybe try disabling the queuing https://hzrd149.github.io/applesauce/typedoc/classes/applesauce-accounts.BaseAccount.html#disablequeue

Also If you set localStorage.debug="*" then it will enable all debug logs which might tell you more.

P. S. The queuing is there because I was sick of Nostr apps asking for hundreds of signing and decryption requests. If it's the issue then maybe it should be disabled by default