What is the problem? Is there any Lua errors?
The pushback mechanic uses wrong values.

What steps will reproduce the problem?
Tested with player casting event "UNIT_SPELLCAST_DELAYED".

Does the issue still occur when all addons except ClassicCastbars are disabled?
yes

Was it working in a previous version? If yes, which was the last good one?
no

Any additional info? If you play on a non english client, please include your locale:
https://wow.gamepedia.com/index.php?title=Interrupt&oldid=305918

Thanks, I'll look into it later. (currently on vacation so gonna have to wait 2-3 weeks)

Edit: Beta is down now, I'll fix this some time after game release.