It looks like the new Views (and it seems to be the case with Blocks as well) is not compatible with the new WordPress 5.3.1... After a lot of searching why I get errors and reinstalling my site, I decided to downgrade to WordPress 5.2.4 and saw that the problem was resolved... I also uprade to WordPress 5.3 and it still works fine. But as soon as I upgrade to 5.3.1, I get a bunch of errors... So, they probably changed a feature or security settings...
You'll find attached the screenshot of my page with 5.3.1 enabled (unfortunately, it's local, but it should help you find out what it is).
The update is now available from the downloads page (toolset.com/account/downloads) and should appear within an hour or so as an automatic update (click the Check for Updates button if it doesn't).