Importent addendum:
Please look in your vm config "/administrator/index.php?option=com_virtuemart&view=config" and check the setting for "Enable Multivendor". Vm2 has a different behaviour according to these settings.
"Enable Multivendor": none
Vm2 has a multi administrated single vendor mode. This means, that in the single vendor mode many administrators can handle the store.
Important is that only one of your Superadministrators is set as vendor. When other administrators log in, then they are automatically mapped to the vendor with id = 1.
Problems:
Somehow the system lost the reference between the joomla user and the vm vendor.
You can see this when you enable the "administrated multivendor" and take a look on your shopper list. Now you see there an extra Column "user is vendor". Here you can enable joomla users/shoppers being vendors. Dont use this atm, it is experimental. But you can see here if there is something wrong with the tables.
In the single vendor mode there should be only one icon green and the rest should be red. Other administrators who should act as the main vendor should NOT be registered as vendors! You will notice, even when they are not vendors, but administrators, then they see in the shop information the data of the user which is activated as vendor and mapped to vendor with 1.
Solution:
You must just take care that only one user is activated as vendor. To achieve this and to be certain to get a mapping to the vendorId = 1, enable the multivendor mode. Go in your users list, enable your desired shopowner as vendor. Before you edit this user now, you must set the "enable multivendor" to "none" again. Then logout,.. login as the desired shopowner, go in the shop config and you should have your vendor tab. Enter your data and store it. The tables should be fixed now. When the problem persists, you must manually fix the tables with phpmyadmin.