by John R.
https://moodle.org/mod/forum/discuss.php?d=215932#p959984
We had the same issue and there is a setting on the web server that defines the max character length for variables. Ours was set to short. Once this was fixed it worked fine. Sorry I don't know where on the webserver and what setting it is since I don't admin the web server. Good Luck.
Edit: It turns out it is in the settings for the suhosin module for php