I want a folder format to automatically sort by date modified with the latest date at the bottom, but even if I reverse the order and save the folder format, it goes back to descending order. Seems like it's the only folder with this problem.
How are you saving the format?
How are you navigating to the folder or opening the window?
Once you're in the folder, what does the tooltip when you hover over the format lock (on the status bar) say about where the current format comes from?
The current format comes from the path format that I set up, it's the same as before this bug appeared, it just changed file sorting order by itself all of a sudden. And the padlock is opened, as per usual.
And it doesn't matter how I navigate to the folder as far as I can tell 
What does the tooltip when you hover over it say (when in that folder)?
"format for path XXXXXXX"
but on second thought I it seems that in the new update the order was reversed for "date modified"? Because that's when the "bug" appeared. 
Oh and I noticed it affected all folders with date modified set
Yes (details are in the release notes).
Any folder formats from the old version which sorted by Date Modified should be automatically adjusted to sort the newest items at the top with the new defaults.
You can re-save any folder formats that you want to sort in the other direction and they should remain sorted that way from then on. (The default sort-order can also be changed back if you want newest items to go to the bottom, instead of the top, the first time you click the date column.)
Oooh well that makes sense then 
thanks