Looks like maven would not build the right path for tests, since it can not load the log config. This could be also the explanation for not picking up the right security provider (bouncy castle). You likely have some unique environment or build of maven. Local hosted repositories or patched?
Or you are running into Windows unable to deal with paths longer than X byte or paths with space in it or similar.
General suggestion:
Install some unix based operating system before trying to build software.
i find your suggestions a bit dissatisfying from a build perspective. You are using platform independent language and a platform independent build stack and yet you are suggesting your actual build may in fact be platform dependent. I understand you have other priorities bringing up the code to a high level of quality, but you should be in the frame of mind where your code and build will be platform independent at some point. PRab swapping out versions of protoc is a perfect example of something Maven is supposed to unequivocally disambiguate. At a casual glance, everything else in the build is looks good, which is why build issue a bit confusing.
I did do some research the other day, and I can see you are including protoc in your build as it has been recommended in various forums. My main issue is that the recommendation is incomplete (some posts even acknowledge this), which is why PRab and I are unable to reproduce your build without a non-trivial amount of effort.
I feel I can contribute to helping you create a platform independent build or at least a clearer build path, so I will try to help you to that end. I'll need to find some more time to look into this and will contact you if I find I need any more information.