seems to be a regression compared to 1.7 or even 9.0.5

a bit tricky - so far I have been only able to do a reproduction case that 'sometimes' fails :

https://gist.github.com/kares/596f5a3648249181373dca2242332613

#<JRuby::Sample:0x1a09f207>
ERROR: #<NameError: uninitialized constant JRuby::Sample>
  org/jruby/RubyModule.java:3309:in `const_missing'
  repro/_run.rb:8:in `block in repro/_run.rb'
#<JRuby::Sample:0x3bf68c46>

HINT: loading seems to always fail from the same thread as the one first hitting the require.