oktober versions treats xlsx files differently

I used the latest version to add the weekly update to one of my dasboards. It reports various errors related to empty cells -null-.

I tried to change the format of the columns to counter this but it simply does not work.

I then reverted back to the late august version (previous one) and everything works normal again.

Can anyone explain why xlsx files are read differently in the latest version, and what these differences are precisely?

Similar issues have ben reported here :

https://ideas.powerbi.com/forums/265200-power-bi-ideas/suggestions/11134581-i-want-to-download-a-previous-version-of-power-bi