Broken animation bones in Fbx exported

Hello there! I have a problem and I hope that you can help me to fix it.

Well, this is the situation, I have an animation rigged horse. (Running very nice). But when I export this animation into FBX I get in a few frames a bad rotation for some bones!

ok let me be graphic!

This is the good animation to be exported.

With this Fbx configuration

Then I import the fbx to a new blender scene and I get a good animation but some frames are broken!! WUUUDDD???

So, what do you think?

Export as FBX text and look at the file and the offending bone, can you determine why it breaks from looking at the source file?

Have you tried unchecking “key all bones” checkbox? with force start and end keys off too?
Are all your bone transforms applied correctly? CTRL+A