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.
KTM- 2014 500 EXC, 2009 690 Enduro R E BMW- 2012 GTL 1600-sweet, 2011 R1200GS Adventure Honda- 2000 XR650R- 2006 XR650L- Yamaha- 1972 XS750 Tracker, 1971 RC5- BSA- 1945 M20, 1969 BSA 441 Victor . The list goes on but why bore you... 16 and counting. Its an attachment issue.