Hi Joe,
Were there any visible errors? Fatal errors like the one we had won’t fix themselves – chances are if it fixed itself is was a server related issue.
If it was only happening on Firefox, it could have been a Firefox issue (PHP errors don’t discriminate between browsers).
Can you email me any recent entries you have in your server error_log to support@generatepress.com?
There’s a few thousand sites running 1.3.06 now and we haven’t had any issues.
Thanks!