WOW, after hours of research I found the solution how to go back.
Maximum entries are 199 – don’t go to 200, there is no way back!
Go to CPANEL, open phpMyAdmin, > Database (chose your one, the main one), >wp_options
Go there and inside wp_options search either a unique term from your post snippets, that is nowhere else on your website or go direct to:
option_id 190105
option_name post_snippets_options
Click “edit / bearbeiten”
You will see a BIG textfile. Make a copy from it and save it in a text editor, that you can paste it back, if you should do some mistake.
Scroll to the beginning of the code.
You will see:
a:200:
Modify this to
a:199:
Then scroll to the absolute bottom of the text. Erase the last entry, it looks something like this:
i:199;a:7:{s:5:"title";s:14:"KTGlobalTitel2";s:4:"vars";s:0:"";s:9:"shortcode";b:1;s:3:"php";b:0;s:11:"wptexturize";b:0;s:7:"snippet";s:108:"Erl?uterungen zu den Kategorien dieser Illustration von der armenischen Künstlerin & Karikaturistin Agnes.";s:11:"description";s:0:"";}
i is the entry number, but it starts to count at 0, so that why this is i:199 and not I.200
Erase all, not just the part between {} but also the first part: i:199;a:7:
After erasing the code will end with }}
On the bottom of the editor you can click on OK, that it saving the modified text.
Plugin will work again, but don’t do more than 199 post snippets.