I find that when you feed wildlife, they become dependent on the food source, prosper, and multiply.
If the supplied food supply ever ends, there will be cruel and unnecessary suffering among that community.
Blue Jays are fairly intelligent birds. Now that some know a reliable food source, they will continue to raid, and inherently teach others.
Had a similar situation with a few squirrels that learned where the chicken feeder was located, inside my chicken coop.
I still have many, many squirrels, but unfortunately, the pilfering did not end until I eliminated the ones who entered my coop.
You need to find a better way to keep them out, or purge the ones who enter, preferably humanly, until the thieves stop.
Perhaps you can fashion lighter flaps for daylight hours, or create a “tunnel” for the chickens to enter that would daunt the timid jays.