hi
for sometime i had the same problem. i think at the time i had the problem of text replacement shortcuts not syncing, apple's servers were caching old versions and never caught up with the current new one.
i don't think that what i was doing on my end solved the problem by itself, but pretty sure that apple changed something on their end that actually fixed it.
but what i did on my end to get it started was to delete all of the shortcuts on all devices. and let that status of no shortcuts stay like that for a couple of days.
then i added one or two on my iPhone and waited for that to sync to my mac.
sometimes, you will notice apple add OMW on all your devices. i found that if i deleted that before my own shortcuts were fully syncing then my syncs would be erratic. so i don't delete that apple supplied shortcut anymore.
what i also did was to sign out and then back in to my iCloud ID, and when doing so used the primary ID on all devices, (not using any secondary alias on any device as the sign in).
with both mac and iPhone all using latest versions for each, there is no more problem and syncs appear within a minute or so.
thanks. good luck.