VSI plugin doesn't work properly for some users

I've been able to register SIS and a couple of Storage systems for me and for a couple other users in vSphere Web client but it doesn't work for some users at all.

It gives me Flash error with code 1009 which is generic Flash error when I am adding Storage Systems.

I also noticed if you go to Solutions Integration Service in Web Client you will see that the Name and the Version have never showed up.

It seems the plugin works improperly for those users for some reason.

I tried to add those users manually on VSI appliance side and give them permissions to the storage systems but they don't appear in vSphere Web Client as well.

I also tried this KB  VMware Knowledge Base  but it didn't work for me.

We are running on vSphere 6.5 U1 and VSI 7.2.

Does anybody have any ideas how to fix it?