Hi @MarkAGregory,
Was any of your content upgraded from OJS 2.x to OJS 3.x? If not, then the quickest work-around for the moment is to remove/comment out the following line in dbscripts/xml/upgrade.xml:
<code function="repairSuppFilesFilestage" />
Then run the upgrade script as part of the normal upgrade process.
Regards,
Alec Smecher
Public Knowledge Project Team