System.Linq not working when published

[rachied]

LINQ methods like Where() do not seem to work when the Playground is published on Github Pages.

Compiling..
Compilation failed with 1 errors and 0 warnings
(26,38): error CS1061: 'IEnumerable<Person>' does not contain a definition for 'Where' and no accessible extension method 'Where' accepting a first argument of type 'IEnumerable<Person>' could be found (are you missing a using directive or an assembly reference?)

Example: https://stryker-mutator.io/stryker-playground/?gist=6c093e492fb2e645bf9636285810c772

The System.Linq.dll assembly is loaded and passed to Roslyn, so this should in theory work.
When running the playground locally, it strangely does work: http://localhost:5000/?gist=6c093e492fb2e645bf9636285810c772