Regen having no effect

[Wulfgang]

Nah, that's not it. I get this often on just standard regen->regen->regen casts. Seems like a server bug. If something is about to wear off, you can't reapply it until it has worn off. That 1-2 second window has something going on on the server.

It occurs when you critical on a Regen cast. The potency of that Regen is higher than a non-crit Regen cast afterwards; as such, you get the "No effect" message when trying to overwrite / extend the duration.