If you have some means of monitoring the current memory requirement I'm happy to keep an eye on it and let you know what user action causing the issue. Alas I didn't record my entire editing session for your perusal. It's proprietary IP anyway, so I'd not be able to release it. I would recommend some regression style automated algorithms that continuously grab random items and connect them together, then delete them, cut/paste, etc. Branch line static testing, scrub back to empty perodicalty and ensure its baseline, etc. That should show something. I'm using the Directed Orthoganol Layout with mostly UML shapes, cuting and pasting between diagrams, moving them about. Not using any groups.
It seems to be fairly reliably dodgy, its the first time I've seen a dialog but the system always seems to slow down after half an hour or so. Gets very slow.
(Don't know why but whilst typing this the form is dropping characters as I type. Then the DOM explorer suddenly appeared just now and it's stopped. Seemed to start after the first gap in the text.)