strange bones rotation in the animations when exporting in FBX for unity I'm trying to export some animations from blender 2.8 but something is going wrong. when I open the fbx preview some animations seem to be broken and others are ok, I tried to change the rotation method from quaternion to euler, something seem to be better but I still have those problems, I tried to see in forums for people with my same problem, there are some but no one of the solutions helped me, I still have this problem, I tried even to see if in the graph editor there are some problems but everything seems to be ok. 
I don't know if this is because I use an IK skeleton with a lot of constraints or it's a bone problem, I'm not really good with blender.
I really don't know what to do, please, if someone knows what to do answer me.
Here are the settings for export i've used:
The problem was the quaternion rotation that was in conflict with the euler rotation (because i changed from quaternion rotation method to euler) and the only thing that I could do is to delete all the quaternion rotation keyframes and recalculate the roll of the bones in edit mode "shift+N" (recalculating the roll of all bones in the right way is important to export and mirror animations) because when blender is exporting in fbx it uses all the rotation keyframes and all the deforming/nondeforming bones deformations so sometimes you may see some graphics artifacts in animations so to avoid this there is an option in the armature tab when exporting called "only deform bones".