I logged on today and where I was getting 723 m/s with Afterburner V, now I’m only getting just above 500. Tried logging/relogging, checked a different fit ship with a different afterburner and checked another character with a similar ship/afterburner. It’s just this character. I haven’t done the math but it’s as if Afterburner V no longer is taking effect.
Just checked a ship with a Microwarpdrive and same issue. Dropped from over 3k m/s to 2.6 m/s This character has Acceleration Control V as well.
Please submit a bug report. This is the kind of thing nobody on the forums can assist with, unfortunately.
Try clearing your client cache in Settings → Reset settings → clear cache. Then relog and try again.
Did you drop from Omega to Alpha? Acc. Control is capped at Level III for Alpha.