Quote Originally Posted by lat9 View Post
OK, I created a fresh install using PHP 8.4.3 of the as-shipped Zen Cart 2.1.0 and copied over the Bootstrap 3.7.7 files.

Made Bootstrap the template and reset its sideboxes to match those of the built-in responsive_classic.

Displayed a product, resulting in no log files generated.
Perhaps ...

Are the sidebox layout settings the same for responsive_classic and bootstrap? Specifically, the best_sellers.

If that sidebox is enabled for the left-column, then it's possible that this (https://github.com/zencart/zencart/pull/7119) post-zc210 PR could correct the issue.