Hi,
The issues you're seeing are caused by a Joomla template override of show_microdata.php from version 5.0.4. When an override exists at templates/<your_template>/html/com_hikashop/product/show_microdata.php, Joomla uses that file instead of the one shipped with HikaShop 6.4.0. So the 6.4.0 fixes for productGroupID, bestRating, and description handling are being bypassed.
The simplest and best solution is to delete the override file. Just remove templates/<your_template>/html/com_hikashop/product/show_microdata.php. HikaShop will then use the updated 6.4.0 version which already includes all the fixes for the issues Google is flagging.
The proposed file you attached is based on the old 5.0.4 code with several issues (missing author validation on reviews, incorrect bestRating calculation, old image URL handling, missing itemCondition on offers, etc.). The current 6.4.0 version handles all of these correctly.
In general, we recommend keeping view overrides to the strict minimum. Only override files where you have actual custom modifications that you need to preserve. The more overrides you have, the more likely you are to run into compatibility issues after updates. You can review all your current overrides in HikaShop backend under Display > Views.