Looks like one more reason for a steering dampener. Been there, done that, luckily without the broken swing arm and shaft. High speed on hard pack then all the sudden it got way soft. I couldn't get back on the rear fast enough. Slap left, slap right and next thing I see is the pig bouncing over me. Walked away too, albeit a bit sore.
2014 KTM 690 Enduro R, 2014 EXC500, 2012 BMW GTL1600, 2015 BMW GS800 Adventure and 16 other motorcycle projects in various stages of completion. It's an addiction thing.