What is the problem? Is there any Lua errors?
Cast bar doesn't react to cast interrupts.

What steps will reproduce the problem?
Your target starts casting spell and then interrupts it, but castbar are still being displayed the cast.

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

Was it working in a previous version? If yes, which was the last good one?
Nope

Any additional info? If you play on a non english client, please include your locale:
Im playing EN and RU locales

This is not a bug, but a Blizzard API limitation in classic. Nothing that can be done about it sadly.