Hello.

So far I could not reproduce this (although I still need to make a test with the precise Visual Studio revision),
Can you please ask the customer to check for version mismatches? Specifically:

1) In Visual Studio, do Extensions -> Manage Extensions, switch to the Installed tab, and select the "QuickOPC" extension. What does it say next to "Version: " on the right hand side?

2) In Visual Studio Solution Explorer, under their project's References:
a) If they are seeing only individual assembly references (so-called packages.config model): select OpcLabs.EasyOpcUA assembly. Then, look into the Properties window (usually below). What is the value next to "Version"?
b) If they are seeing also packages (so-called PackageReference model): right-click References and select Manage NuGet Packages. Which version does it indicate for the OpcLabs.QuickOpc.Forms package?

Thank you