Historical plugin and theme data causing problems?

I’m running a private organisational intranet and until the week before last all was working perfectly. I believe the problem has started after testing some new calendar plugins for resource management (note: I understand the Timely All-In-One Event Calendar can cause some serious problems and it was one of the plugins tested) the page with the Gravity Flow Workflow Status shortcode has developed issues: the shortcode only shows the header bar of the status table now, unless I deactivate BuddyPress (not an option to leave it deactivated), and the menu and primary header do not display on that one page at all. I’ve changed the theme from a child theme of Optimizer to Divi this week which I thought may resolve the issue, but it has not. I have recreated the site on InstantWP, included all plugins currently installed on the live site and set them to the same status (active/inactive), and have done the same with the theme (all other themes have been deleted on the live site as well as on InstantWP). The recreated site is working perfectly on InstantWP. I suspect that there is historical plugin/theme data stored somewhere that I can’t see or haven’t looked. I’ve run WP-Optimizer, including transient options, and no improvement.

Suggestions?

Thank you.