Okay, after more test I'm a bit lost.
Compiling from command line with --debug==release|debug give a segfault when it call findOne from a MongoCollection.
Compiling from monodevelop (using CTRL+F5, because the "play button" didn't do the job well...) in debug|release it run fine until some time then it hang again with a segfault when it call findOne from a MongoCollection.
I give up. To much wtf problems around the place, dub, package, dmd... Please forgive this thread.