The RIFT team spent time over the past several days (including the weekend), chasing down trails left by the Ability Lag Monster. They have some leads under review and we will update everyone when we get them nailed down and ready to patch.
In the interim, relogging usually helps clear up the built up ability lag.
This creature chiefly affects the Prime service, but we anticipate that any fix will also be applied to the Live servers and should help there too!
[I have made this the official thread for all responses, to keep discussion in one place, as this affects players in both services and not all Live players can post to the Prime section.]