[dsp1234]

users should never have assumed it would be stable in the first place.

It's not an assumption. It's directly in the documentation.

"If the same seed is used for separate Random objects, they will generate the same series of random numbers."[0]

[0] - https://docs.microsoft.com/en-us/dotnet/api/system.random

[iainmerrick]

Read just a little further:

“However, note that Random objects in processes running under different versions of the .NET Framework may return different series of random numbers even if they're instantiated with identical seed values.”