If you have Stackable installed and activated and you are encountering an error in your Block Editor that say: "Your site doesn't include support for "ugb/X" block", then please try the following solutions:
Do a hard refresh on your browser by holding the shift key while reloading the page (SHIFT + F5 for Windows or SHIFT + ⌘ + R for Macs), or
Try clearing the cached files from your browser privacy settings
This usually is a browser caching issue, and doing the above should force your browser to load the latest Stackable plugin files. If the above fixes do not work, please contact our support team and we'll see what we can do to help.