I have a similar problem with the router.
Menu links to categories work normally, but links to the products don't. Instead of having the product URL as href, they have the category URL.
This happens only with SEF enabled, regardless of URL re-writing, and only when the product has its own dedicated menu item.
Joomla version 4.1.4, Virtuemart version 4.0.0.10645. (that's the latest version available on virtuemart.net today... Not sure where kiro789 got 4.0.2.10661 from)
The bug has two unwanted effects. If you visit the category page (e.g. virtuemart/headpiece/), the product links inside the category that have dedicated menu items of their own show the category URL as href instead (again virtuemart/headpiece/ instead of virtuemart/headpiece/safety-helmet).
If you visit the product page (virtuemart/headpiece/safety-helmet) by using the dedicated menu item, you see the category page, while the URL is still correctly the product detail URL (virtuemart/headpiece/safety-helmet).
Hope this helps.