Hi,
I don't know why it has changed to "default" after upgrading. Your VM Config file must have been refreshed (it shouldn't have been though)
Did you check the individual categories and made sure the "Default Product Details Page" is set to "flexv2" or to "no override" ?
Attachment Pasted_Image_1_10_13_12_33_AM.gif not found
Furthermore, you can check individual product, and make sure "no override" option is selected for each product.
Attachment Pasted_Image_1_10_13_12_36_AM.gif not found
(selecting no override, means, what ever you choose through VM Configuration will be valid for those categories and for those products. As it says; there will be "no override")
Regards.
Forum Support.