Try this:
1) Clearing media cache will NOT fix this issue fully. Some of you may have good luck, but not me on Win10 latest version.
2) Easiest and quickest workaround (after much too much research) is to:
a) open or re-install premiere pro CC2017 by launching CC app, using the down arrow and selecting "Other Versions" and choose cc2017 and wait for install. It will install pp2017 and media encoder 2017.
b) If you've been working in cc2018 and suddenly your files are out of sync, do not despair. From you CC2018 file, export to Final Cut Pro XML (File|Export|Final Cut Pro XML)
c) Open cc2017 and open this xml file. Check your sequences and they should be in sync.
NOTE: You'll probably loose all that new, cool functionality from cc2018, but hey, at least you don't have to go back re-cut ALL your work.
I hope this helps.