Product page looking funny after upgrade to 1.3.9f

I upgraded from 1.3.9d to 1.3.9f. This was for a site I did not create.

Everything seemed to go fine but then the client pointed out the the product pages were not behaving correctly.

The designer had customized them so the thumbnails were clustered in a square pattern and clicking on the thumbnail caused the main picture on the product page to be replaced.

Here's a screen capture of the correct layout.

Once I upgraded it laid out the thumbnails in a vertical pattern and then when the thumbnail was clicked there would be a pop-up window with the big image; which I was told is the default setting for the product page.

Here's a cap of that layout. (Note: this actually was produced in Photoshop after reverting to 9d, so it's not exact but very close)

Anyone have any ideas as to what would make this revert to the default setting?

Thanks!

If you still have a file backup of the original
Compare the currently used tpl_product_info_display.php file to each copy of that file you can find in the original.....

Odds are that it was customized by the individual and they did not use the templat override system and the customization was lost on upgrade

Adding a link to this would have assisted

Apologies. I got caught up in the screen caps and forgot the link.

https://www.baileydoesntbark.com/shop/index.php?main_page=product_info&cPath=306_336_348&products_id=289

Are you saying that if I replace the tpl_product_info_display.php with the one I have backed up it may fix this?

Are you saying that if I replace the tpl_product_info_display.php with the one I have backed up it may fix this?
What I am stating is that you should use a dif program to compare the differences....
Depending on where/path in the backup you find it- - if different - - use it in the proper template override structure