A total loser works for a ruthless Vegas casino boss to jinx gamblers. But after he falls in love with a cocktail waitress, gamblers become winners instead. Now he must save his Lady Luck from the boss’s murderous wrath.

I think your version is pretty good. One sentence makes it clunky; this is as far as I could get-
When love debuffs his jinx, a hapless employee must save his lady from the ruthless casino boss

A favorite film, but a challenging one to logline.

I elected to break it up into 3 sentences because one l-o-n-g sentence is cumbersome, too hard to read.

Setup, hook: A total loser works for a ruthless Vegas casino boss to jinx gamblers.

Inciting incident, plot twist/reversal of fortune: But after he falls in love with a cocktail waitress, gamblers become winners instead.

Objective goal and stakes: Now he must save his Lady Luck from the boss's murderous wrath.