TOPIC:

When I want to save the LO web server reports an error. I do not know where to look for a mistake? Is there a problem with code in a file (JSON)? LO is quite extensive. Is there a problem in the web server file size settings? Problem occurs only with one of LOs. Thanks for the help.

The best place to start is the error log of your webserver, i.e. apache.

It has nothing to do with the json files you list in the second image (and these are quite old anyway).

If there is no error in the log, you coudl try to enable verboser logging by setting $development to true in config.php (by editing the file, around line 43)

Have you installed the php-xml package? (for linux distributions)
this did the trick for me