It is very possible that you have issues with Theme itself as Baristern Joomla theme is it is almost 5 years old theme, Try putting site to offline mode disable plugins one by one and locate one with incompatibility, then try to enable one by one.
I had such issues with various old themes based on Helix and SP page builder and for some I ended exporting all pages with SP Page builder, Installed latest versions and imported pages. I was lucky in most cases I had no more than 15 pages.
