grapheme_substr: length is beyond start
It is version 126.96.36.199
You are using an older version of concrete5. I would make a full site backup (database and files) and see if updating to the latest 188.8.131.52 resolves the issue.
If it doesn't fix the issue, I would temporarily enable debug errors and reply with the full error and an error screenshot.
Dashboard > System & Settings > Environment > Debug Settings > Error Detail > Show the debug error output