Disclaimer - I'm not an expert, but usually do have an opinion...

I've watched it several times, but I'm not sure there is enough information to really make a call on this one just based on a poor cab video copy.

Note that it's the left rail that suddenly pops up into the air. I have seen a vertical sun kink that was caused by one rail that raised the track hip high. If loads were being run the opposite direction and they had bunched up the rail at the crossing, then it makes sense they might have had tight rail there. If the next crossing was fairly close, they typically anchor the rail rather than let it run. The track squirreled out way to far to have just been from a sun kink, so I'm thinking the lead unit had already dropped and was bunching the track up ahead of it. Other possibility might be a broken left rail under the lead unit.