Tons of local SEOs are reporting seeing a notice in Google My Business for "missing store code" for listings. Justin Mosebach posted in the Local Search Forums "Just checked the dashboard in Google My Business this morning and noticed that all of the locations (for multiple clients) are suddenly missing store codes." He is not alone, this is widespread.

Here is a screen shot of this issue from Steve Plunkett on Twitter:

Tons of Google My Business listings are having this issue - but you do not need to worry because you are not alone. It must be a Google bug and I wouldn't bother trying to fix it if it just started happening yesterday.

Forum discussion at Local Search Forums and Twitter.