Hey, I had the same Issue, and I finelly could Fix it.
As I see, it is not a problem with an specific version of the operating system. It could happen with any update.
I had my 3 devices (Macbook Pro, iPad, iPhone) syncyng properly until one day I noticed the list of the Text Replacements in the macbook was missing, but were still showing in the iPhone and iPad.
I noticed that if I added a new replacement or modify an existing on in the iPhone or the iPad, it would show on the other Device, but not in the Macbook, and just sometimes, if I added a new replacement in the macbook, it will show on my other devices, sometimes as duplicates (in some occations i had to turn off and turn on the iPhone or ipad to make to see the new modification ). However if I modify something in the iPhone or ipad, it would affect the macbook.
This is what I did to fix it:
1. I created all my text replacements in the macbook pro from 0. (some of them where showing as duplicates in the other devices).
2. I made a back up of them by selecting them all and dragging them to the desktop of the macbook.
3. I deleted ALL the replacements from the list in the macbook.
4. I deleted ALL the replacements from the iPhone (i verify that in the ipad were also deleted).
5. Once i had no text replacement on any Device, i dragged my backup to the list on the macbook.
6. I turned off and turned on all my 4 devices (I did it just in case)
7. Now my 3 devices had the same text replacements, and any modification made on any of them was syncing perfectly across the macbook, ipad and iPhone.
I strongly recomend to have a backup of the text replacements in your macbook, cause this error I believe could happen with any update.
I hope this work for you guys.