Migrating project from 5.1 to 5.6, increase Android .aab size by 100 MB

I just migrated my beautiful new game project from 5.1 to 5.6,
that worked after some issues, but when packaging, my final Android package size increased by about 100 MB and that is just from migration and i did’nt change anything in the project settings.

This sets my total .AAB file size to 300MB and i can no longer push an update on the Google Play Store.

I am wondering what might be causing that size increase?

One thing comes to mind that 5.1 and 5.6 might have different defaults for certain settings which affects texture seizes, but i am not so sure about that?

Any thoughts on the matter are highly appreciated.