The connection issue with idsera was finally resolved after I added a few more relays, in addition to just nsec.app. This leads me to believe that the root cause might not be with amber or jumble themselves, but rather an unstable connection to a specific relay.
To help narrow this down, I have a couple of questions:
Do other apps that use Amber for login, such as coracle or primal, experience the same connection problem?
Does the same issue occur with the web version of jumble when used on a PC?
As a side thought, I wonder if using a local relay app on the phone, like nostr:npub1hqlxlq57nvlq70ugmsmu9y5lmyc5k2lh5w7y85j7dgsr5u7zwavq5agspw , could potentially mitigate the problem. Of course, I'm also concerned about the user experience of asking someone to install a whole other app. However, since this issue seems to affect only a small number of users, if this is confirmed to be a reliable fix, we might consider suggesting it as a workaround specifically for those affected.