Duplicating pages in Cornerstone with Yoast Premium activated

Hi, Themeco.

I’ve run across a conflict between Cornerstone and Yoast Premium.

When i duplicate a page in Cornerstone with Yoast Premium activated, I get the following error:

This has been true for all duplicated pages in Cornerstone i’ve made over the last, say, week. I’ve just deleted most of them. But i still have these two:

If i turn off Yoast Premium, i can duplicate pages with no problem and can then still use them even when Yoast
Premium is turned back on. These two pages are an example:

I’ve turned off all of my plugins except Cornerstone and then turned them on 1-by-1, as has Wordpress, my host. So we know that the conflict is with Yoast Premium. I’m running v. 23.8 of YP. And i always keep my X and Cornerstone updated (currently running version 7.5.1 of Cornerstone).

I’ll send you a secure note shortly with my login info.

Thoughts on what might be going on?

Thanks, as always, for your help,