Paket > 5.4.8 does not work with Klondike 2.0.0 anymore #2504

Description

I use two NuGet remotes: an internal NuGet server running Klondike 2.0.0 and nuget.org. Paket versions between 5.5.0 and the latest (5.5.3 currently; I can't get 5.6.0; was it unreleased?) When I went to run

paket outdated

or paket remove... then I get an error like:

Paket failed with:
-> Unable to retrieve package versions for 'Foo'
-> Could not find versions for package Foo on any of ["https://www.nuget.org/api/v2"; "http://nuget.internal.local/api/odata"].
        -  Source 'https://www.nuget.org/api/v2' yielded (0): []
                -  Request 'https://api.nuget.org/v3-flatcontainer/Foo/index.json?semVerLevel=2.0.0' finished with: []
                -  Request 'https://www.nuget.org/api/v2/FindPackagesById()?semVerLevel=2.0.0&id='Foo'' was skipped because 'ProtocolNotCached'
                -  Request 'https://www.nuget.org/api/v2/Packages()?semVerLevel=2.0.0&$filter=tolower(Id) eq 'foo'' was skipped because 'ProtocolNotCached'
        -  Source 'http://nuget.internal.local/api/odata' yielded no results
                -  Request 'http://nuget.internal.local/api/odata/FindPackagesById()?semVerLevel=2.0.0&id='Foo'' was skipped because 'ProtocolNotCached'
                -  Request 'http://nuget.internal.local/api/odata/Packages()?semVerLevel=2.0.0&$filter=tolower(Id) eq 'foo'' finished with error
                -> Could not retrieve data from 'http://nuget.internal.local/api/odata/Packages%28%29?semVerLevel=2.0.0&$filter=tolower%28Id%29%20eq%20%27foo%27&$skip=20'
                -> WebException: The remote server returned an error: (404) Not Found.

where Foo is the name of one of my internal packages and nuget.internal.local is the name of my Klondike server (actual names differ; these are replaced). This prevents me from using Paket for anything that requires interrogating versions.

When I manually run a GET against http://nuget.internal.local/api/odata/FindPackagesById()?semVerLevel=2.0.0&id='Foo', I get results, as always. The Klondike server is up; I can browse it.

I have been using Paket with this internal NuGet server for 15 months without any problems, and when I revert to Paket 5.4.8, the issue goes away.

Expected behavior

Still be able to use packages on the Klondike 2.0.0 server.

Actual behavior

Paket errors out on practically anything but restore.

Known workarounds

Revert back to Paket 5.4.8.