Paket pretty much always deadlocks since 0.38.
The issue pops up as soon as you delete the cache and are on linux.

Repro:

git clone https://gist.github.com/d8653537d65775db669c.git
mono paket.bootstrapper.exe
rm -r ~/.local/share/NuGet/Cache
mono paket.exe -v restore # deadlock
# if you cancel the above and try again it will work

The last message seems to be different depending on the mono tracing flags. However is seems to be always near the FSharp.Compiler.Service License, after 2 previous 404 warnings.

I tried out the last few versions of Paket until the build started working again, see here: https://travis-ci.org/matthid/Yaaf.Shell/builds. I can repro this on my local gentoo machine as well.
Windows is not hit, as you can see here: https://ci.appveyor.com/project/matthid/yaaf-shell/history

Note it is also possible that the default timeout is >10 minutes (or longer on mono) and that's the reason why travis kills the process (I did not try to wait a day to see if it eventually finishes..)

Or this could be some mono race condition bug we should IMHO work around somehow, if possible.
That said: Can somebody reproduce this? Should I try to send a fix for this?