Problem with saving large data

Can’t save page if content data is over 50k. Currently don’t have time to debug.

Used plugins – only SQLite.
Used template – default wordpress.
Config changes – nothing.

What to do:
1. in notepad (or other text editor) create large data with some shortcodes – like very large single page.
2. Paste it in single page and try to save.
3. No changes – page is blank.

Exceptions:
Sometimes size of data that won’t save is below 50k (even 5k) sometimes can be above. Propably depends on servers resources.