Mac App Store not showing updates

The Mac App Store app has stopped showing (pending) updates, and for the past 4-months I've had to manually go into each app summary to see if an Update is available. From there, everything updates fine, but it never shows as Recently Updated. I've done all of the suggestions in Apple's support documentation (sign-out/back in; restart my iMac (with latest OS updates applied); date/time correct; credit card info correct.

Is there a file that I can rename/delete to force a rebuild or something? Thanks for your assistance!