I am using joomla 3.9.6, VM 3.4.2, and PHP 7.2. Whenever I go to add to add a new product, fill in all the fields, and save, all the fields are wiped out and nothing saves. It is as if nothing was recorded. I also can not cancel or leave the new product one I start to create it. The only way for me to currently add a new item when I clone from a previous one.
Have you tested using php 7.1 ?
But it's as you have a javascript problem. Standard back-end template, module ... ?
Yes I have switched between php 7.1 and php 7.2 but still having the same problem. I have two other sites that are identical and are working fine just this one isn't working.The backend is standard and the theme is Vermilion from Rockettheme
Hvae you set error reporting to none ? If you have a PHP error(or warning) this get send to the display and can break the script.
Check your Joomla configuration about error reporting and set it to "none" and check if it work.
clear your Joomla cache after that, to be sure the error message is not in the cache because Virtuemart use the cache in Back-end.