VS 15.8.1 update causes "Package is not compatible"

[s0ciopa7h]

After upgrading to VS 15.8.1 "Package is not compatible"
MahApps.Metro version v1.6.5
OS: Win10 1803
Visual Studio 2017 15.8.1
.NET Framework : net40

[QuantumDeveloper]

Its not 15.8.1. I have 15.7.5 and see the same issue.