Performance declines after packaging

I am making a plugin using multi-threading.
In the editor, I checked that it worked, but when I packaged it for testing, I found a problem.

I couldn’t check the main game thread, but at least the multithreaded performance was 10-20 times slower.

When I checked the detailed performance results through time measurement, it was the same (10-20 times) slower on average for all codes.
Even if I changed the priority of the thread, the result was the same.

Can I know any information or solutions I can get?

To be honest, I think it makes no sense that the multithreaded performance declined when packaging was done.
But this really happened, and I have to fix it, but I don’t even have a clue.

ps)
I made a plugin using FRunnable.