I suspect that it can have many causes.
If, for example, your links to social networks compare, do these links to the products still work, are the images still displayed?
If the SEO data after the change to TB still exist, they may have to be re-entered?
Probably there is also a problem with the template, that Google previously looked at this better than now.
Have the page load times got worse? (possibly at the same time a server change)
etc