Thanks for following up. Yes, the good news is that I was able to generate a new Post Grid block from scratch with identical settings to the old one and the new Post Grid blocks worked great. Even publishing the two blocks side by side in my tests the original Post Grid block that went through the plugin update still showed the buggy auto-generated excerpts. But the new Post Grid block I generated today worked great and showed the manual excerpts.
In short, I went and deleted all the Post Grid blocks and then replaced them with new ones from scratch and everything is now working fine again. So whatever bug happened was unique to the process of updating an old instance of the block during the plugin upgrade.
Hope that clarifies things if it happens to another user.
Jake
