On my shadow priest, I've tried a handful of community macros and my own, Vampiric Touch in a cast sequence command will sometimes get stuck spamming the Vampiric Touch spell and not rotate to the next spell in line.

It occurs most commonly when tabbing through new targets trying to dot a pack of mobs. What resolves the stuck macro is manually casting a new spell. Sometimes after manually casting a new spell the castsequence will cast 1 last Vampiric Touch before continuing sometimes it continues immediately.

Thanks

Castsequence is buggy outside of Blizzards set scenario. There is nothing that GSE can do about it as Blizzard won’t fix it. It has been broken since Legion and this is one of the scenarios where it is broken.

All GSE can do is pass the command over
To WoW. It has no control over how WoW executes it.

I’m afraid the only solution is to look at your macro and find a different way of doing what you want to achieve.