Site with single page theme applied to all pages outputting Gutenberg content to the bricks ”post content” widget.
If I edit any Gutenberg content only page using bricks (Often just to edit theme settings etc) and then save with no bricks content, then the page is changed to render with wordpress in the front end. Only happens if there is no bricks content.
If you mean “Single page template”, what do you have inside? Just “Post Content”, what do you set as a source?
Maybe you can record a quick video of the setup?
I can replicate the issue though, in some way, but I would love to test with your setup as well, before I create internal bug report.