I want to export images and preserve my Lightroom keyword hierarchy if and when I re-import that image in to Lightroom. It's my understanding that checking the "Write Keywords as Lightroom Hierarchy" will preserve the hierarchy of the keywords. However, when I export with this box checked and then re-import that file, all the nested keywords, synonyms, etc. are all treated as top level keywords. Which pretty much totally messes up my keyword list.
What could I be doing wrong? I am not using any export plugins. I'm on Lightroom Classic CC 7.4
I just tested this and it works in my LR 7.4. As a next step, I suggest uploading a sample exported photo to Dropbox or similar and posting the sharing link here. That will help narrow down where the problem is.
Also, note that synonyms will always get reimported as top-level keywords -- that's been a long-standing problem with LR for years.