I've got this error before and reported it (https://toolset.com/forums/topic/wp-conditional-fata-error-stops-page/). It never really got resolved but I found a workaround to get around it. I didn't know if it was something strange with my code or setup at that point.
However, I got this error again and it seems much clearer to me this could be a bug in Toolset. It's also quite serious since it locks the whole page and you can't even roll back to a previous version. Unless you deactivate the Toolset Blocks plugin (the workaround).
The only thing I did to get this (on a previously working page,) was to add a Conditional block in the loop of a View. This conditional block tested if the posts body content was empty. I could then save the page with the new conditional statement but never load it again. Not in editor mode either. No other plugins (when deactived) affected this expect the Toolset Blocks so I think you should take a look at this since it seems to be a bug.
Hello,
In the post content, you need to avoid to use [wpv-post-body] shortcode as the condition of conditional block, it will conduct unexpected result: Endless loop.
You can try other workaround, for example:
https://toolset.com/forums/topic/conditional-output-if-the-post-content-is-filled/
My issue is resolved now. Thank you!
Custom function works however I don't think it should hang when using the [wpv-post-body] shortcode either.