Some Homebrew formulae (casks) require CLI intervention when upgrading (for example, I am aware of dotnet-sdk, virtualbox and vagrant). Their installers require the administrator password in order to uninstall/reinstall components.
When these are installed on a system, Brewlet will still run an update, but will endlessly show that it is updating because these prompts are never shown or responded to.
Not sure what the best option might be for handling these.