Ok, then it is for sure most likely the antispam protection on the registration form doing this. I've no idea why it only affects those select number of users though. It's possible they left the page sitting for so long that the cookie expired maybe. I don't know what to suggest other than completely remove the check in the core code. We normally don't suggest core edits, but again I don't know what else to suggest since there's no reliable way to repeat the issue in order to debug it.
IN: components/com_comprofiler/comprofiler.php
ON: Line 967
FROM:
Code:
cbRegAntiSpamCheck();
TO:
Code:
// cbRegAntiSpamCheck();
Have added a feature ticket to see if we can redo this behavior to improve its reliability.
forge.joomlapolis.com/issues/6978
krileon
