I am experiencing this also -- hugely frustrating (550 page document, takes about 45 seconds to complete a "save").
I noticed one thing of possible interest: After starting the save, if I go to File->Info, in the Inspect Document section mid-way down the page it has an active spinner which says, "Searching for issues". To the left is a "Check for Issues" box which opens
a page with a bunch of checkboxes, but unchecking them doesn't seem to have any noticeable effect (FYI, if you try this, try unchecking all except for one -- if you uncheck all of them your changes won't stick).
Ick ICk ICK!
Barry
P.S. Word got so confused when I did the above (unchecking all but one box, then trying a save), that it got stuck "Searching for issues" and never returned. At it's prompting, I had to restart it -- when it came up, it opened "Document1" (rather than the
document I had been working on). I closed that and reopened my original document and now the save time has been cut in half (about 20 seconds), though the checkboxes are all checked once again.