Updated Nimble Page Builder to version 1.10.9.
Disabled all plugins except Nimble Page Builder.
I cleaned the cache. I tried it in other browsers. Problem still exists. If I add a block, it is not visible. And when saving 503 error.
This reply was modified 2 years, 9 months ago by OlegBon.
The fact that you see “This page uses a custom template” is normal if you use Nimble Builder template.
What’s not normal is that you cannot edit anything on this page.
I don’t know how to help unfortunately because I can’t reproduce the problem when using Nimble Builder + Customizr theme, with the latest version of both, and latest version of WP.
In addition to the troubleshooting steps for Nimble Builder ( in particular the check for plugin conflicts ), you can also try to switch theme, and verify that you don’t have a mu-plugin active that could break things.