This bug is quite annoying!
After investing a considerable amount of time and effort into creating a new multi-select property and re-assigning all options I need (as a replacement for the old one, which could no longer be sorted), that newly created property turned out to have become corrupt too, so the options cannot be sorted manually; any changes made using drag & drop produce chaotic, unpredictable results.
The only thing that works is to drag an option to the top of the options list, where it will remain; but any other movement of an option will fail and mix up all the sort order of the options in an unpredictable way.
The only thing I can do is search for an option, but I cannot use the list because it cannot be sorted.
I must admit that I am a little annoyed.
So my question to the community is: does anyone else have similar problems with manually sorting options of multi-select properties?