Very curious, since the initial release of Office 2016, it has been version 15.xxx all the way up to 15.41 in December 2017, and now suddenly a jump to version 16.9 (not even 16.0 but .9). I noticed immediately after installing 16.9 that it ran MUCH slower than 15.41. SLower to launch, slower even just scrolling through long document, slower search. Did a search for a word I knew existed in the doc, it found 0 matches. Reverted back to 15.37, immediate and obvious speed up back to 'normal', and the search for the word found the match, no problem. This version 16 feels like 'fast track' release, not a stable. Strongly recommend you stay on version 15 until this gets worked out. If you upgrade to 16 and then decide to revert to 15, downgrading is fairly straightforward, but you will get an error after restarting version 15, that the app cache is corrupted. DONT restart 15 (after the delete of 16) by attempting to load a working document, just launch app, because program will try to reload previous open doc and attempt to 'recover' because it thinks it is corrupted. In hindsight, before restarting 15, I should have used Onyx to clear the application cache.
UPDATE: confirmed after doing some googling, this 16.9 was Insider Preview 'slow' release on Jan 8, and then released to 'stable' general release on Jan 18. 10 days between release to the 'slow insider' group to general release is very fast. Definite screw up here by Microsoft. Many of the Online comments by insider reviewers noted the slow down in speed and BLASTED Microsoft for releasing 16.x to the general public just 10 days after release to the insider group, even though insider users had complained about numerous issues since 16.0 (point zero) going back to early December. Apparently a 16.10 came out Jan 22, but apparently still has major issues, particularly 'slowness'.