You need to enable debug mode. You can use environment variables on the webserver. Are you working on a local server or an online webserver? That link also describes how you can enable debug mode with your .htaccess file. If none of the above work for you, you can put

putenv('FORK_DEBUG=1');

on top of the index.php file in your root directory. This will enable debug mode.

Debug mode will disable cache and it shows error (if there are any). It also sets "noindex, nofollow" on every page, so don't use debug mode on a live website! Google won't find your website if you use debug mode (noindex, nofollow).

Thanks, helped only a: putenv('FORK_DEBUG=1');

Great :) Don't forget to remove it after you publish your site online

Certainly!

Strange thing, switched putenv('FORK_DEBUG=1'); Now when I disconnect this mode, the site does not open at all, shows a blank page

Hmm try clearing your cache folders... Maybe it tries to use old cached data. Strange...

Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 33389407 bytes) in /public_html/vendor/spoon/library/spoon/exception/exception.php on line 441

I do not understand what was going on, cleaned the cache, but it still gives an error Fatal error: Allowed memory size of 134217728 bytes exhausted

Strange. Too bad the exception doesn't indicate which code is taking all the memory?

How to track that suggest?

Fork CMS 3.8 doesn't use the Spoon error anymore but uses the Symfony error page, and that's very detailed. But I guess you don't want to upgrade :-)

I have is 3.8.1

I had that too. It was solved by clearing the cache using the remove_cache script.

I understand this script here https://github.com/forkcms/forkcms/blob/master/tools/remove_cache but what if your hosting does not allow scripts to run, is there any alternative to php?

Friends thank you all, especially John Poelman connected to ssh and performed cleanup script, it worked

If your host doesnt support ssh, then just empty all the folders written in remove_cache script manually...