the past 3 versions there is a 20-30 second freeze when opening the inventory first time after loading a world. Version 1.3.8. also crashes afterwards: https://pastebin.com/wuQdnjcS
I do not have lucraft installed and have disabled skinchanging if this matters.

So does this only occur with skin changing disabled?

This happened to me too once while testing (with skin changing disabled). My guess without looking at the code is that it tries to do some texture stuff because of the inventory rendering, but because skin changing is disabled it gets an NPE or something.