Periodically doesn’t unlock. Buggy

I’m not sure that updating the plugin is the only cause, but it is a cause of this problem: the correct password ceases to unlock the content after an update and says “security check failed” or something when attempting to authenticate. This causes a periodic freak-out of my customer. To fix it I have to add and take away the whole-page lock…I think… It’s hard to pinpoint what I actually do that makes it start working again.