Can’t edit snippets or create new ones

I’m unable to edit or create new snippets, although mere minutes before this problem occurred I was able to edit a snippet. So, it’s not a problem caused by some recent update.

When I make changes and click Update, nothing changes. Similarly, when I try to create and save a new snippet, I’m just bounced back to the creation form/screen. No snippet is created

Probably, it’s a plugin conflict. (It’s not a browser extension conflict because I tested for that.) But before I go through an arduous and all-too–common process of elimination, maybe someone can suggest a likely culprit? Like the kind of plugin that might be interfering with WPCode?

Thanks.