Page editing problems

Over the last few days I have had trouble with this specific page on my site:
When I try to edit the page it locks up and crashes. I've tried it from three different computers and two different internet connections. I have tried deactivating virtually every plugin and have the same problem. I contacted the theme company (themify) and they say they can't recreate the problem.
If I change from my preferred theme (Landing) to a default simple theme, I can edit the page without a problem. When I switch back - the problem comes back.
Hoping you can help. thanks!