brew cu doesn't update properly latest version of app

[yannpub]

For an unknown reason, one of my macs isn't updating properly the latest version of the apps.

As an example, as of today, latest version of firefox is 91.0.1 and is shown as such on my Mac #1 and is getting properly updated
On the other hand, if I run brew cu on Mac #2, the latest version is showing 90.0.2
This is valid for also other apps.

To me it looks like the 'list of latest available versions' is not updated properly

Has anyone some suggestions (files, folders, configs) I should look at?

[yannpub]

Fix:
git -C $(brew --repo homebrew/cask) checkout master

My mistake, Brew was not on the default branch anymore - Nothing to do with homebrew-cask-upgrade.