When using BlueOcean interface, the interface generally responds quickly. However if there is a problem contacting the Jenkins backend, the UI will either appear to be waiting, or claim to have completed whatever it was doing instantly.

Simulating: I have my Jenkins behind a VPN, if I switch off the VPN then the BlueOcean UI does not notice. This could probably be replicated by stopping the Jenkins server (although it might be a slightly different failure).

The reason I noticed it was due to favourites - I'd disabled the VPN, and then I clicked to favourite a few items. The favourite star went yellow, but there was no feedback in the UI that the favouriting had failed.

Feel free to rewrite this as a specific favourites issue.