Page Title Changes Unexpectedly

My website using Coller Pro has been up for 2 years and the content updated frequently; new posts or page modifications created to keep the site fresh. No significant issues until recently. Running WP ver. 4.8.2 using Coller-Pro theme.

Lately, when editing a page/post or creating a new one, the page title that I give the page will inexplicably change to that of a recent post that I had created weeks ago. The associated permalink also changes. I can change back, but if I modify the page further, the title/permalink reverts back.

I don’t think this was tied to an upgrade to 4.8.2; nor have installed any new plugin nor the latest version of Coller Pro

Any ideas??