We have had an incident last week whereby the Consent Flow would not succeed for some Custom UI apps (see: App authorization requires manual refresh).
In some cases, the requestJira or requestConfluence of the @forge/bridge methods appear broken. In order to fix it, you can revoke the existing app permissions via the Admin page of your Atlassian site.
There, you can go to Connected Apps → Select your app → Manage → Select the user having trouble with the app → Revoke permissions
When this is done, the user will be able to re-trigger the Consent Flow and the auth token retrieval should now be resolved.
Hope this helps.
Sorry for the inconvenience caused.