Why do we see 503 ServiceUnavailableException errors after updating Browser UI (BUI) Extension customizations?

Environment:

Agent Browser UI (BUI) Extensibility Framework

Issue:

When BUI Extension customizations are updated while being used this can cause request to not able to obtain needed locks on the application Add-in/Extension Cache. This will happen if the Extension changes are published in Extension Manager when this cache is also repopulating at the same time. This can cause the cache to be locked and the request will fail with a 503 ServiceUnavailableExceptionerror, and this is expected behavior.

Resolution:

To avoid errors such as this is it is best to update BUI Extensions during off hours for the site and/or to have users logout and then log back into the BUI console after extensions have been updated.