The file copied from Illustrator to animate will be particularly stuck when opened again

The vector characters and scenes used to make animations are drawn in Illustrator, but the files made with these materials are abnormally stuck when opened again. This is a problem that has troubled me for a long time. Does anyone know the cause of this problem?
When making character animations in an, everything is normal, but after the production is completed, opening the file again is very slow, which makes people anxious.
Checking the file, it is found that these materials from Illustrator always have many groups of internal nested symbols, many empty symbols, and these files have no filter effects.
For example, it often takes more than a minute to open a 17M fla file, which is unacceptable.

The system is win11, and it has nothing to do with the software version. I opened it on 21/22 and it was the same。

But if I break up and regroup these Illustrator assets, especially removing the nested symbols within the group, the situation will improve somewhat, but it is obviously not suitable for manual adjustment one by one.