As for com.clearly-useful.generic-collection-interface,
I have tried it several times:

(ql:quickload :com.clearly-useful.generic-collection-interface)

But it loaded OK, without errors. I guess the problem might been 
caused be some kind of race condition or alike.

I'm not sure why com.clearly-useful.generic-collection-interface would be failing…
it doesn't create any threads just by loading. It defines one function
using lparallel's  defpfun in the file parallel.lisp[1], but won't call it unless bordeaux-threads
is fully supported (present in *features*). Is merely using defpfun enough to cause
a problem? I've updated the git repo to disable using it at all if full threading support
isn't present, but I don't know if that's the exact problem here.

parallel.lisp with conditional added: