Shouldn’t be surprising given that there are a lot of retired special forces vets and there are always going to be a certain percentage of bad apples, some of whom were booted out early or later for that reason.
Seems like there would be legalese in a military contract, SF or other, prohibiting a US military-trained soldier, airman...from aiding and abetting a foreign force detrimental to USA interests.
Doubly so if these forces are actively engaged against any US agency or US civil force. They should be classified as terrorist actors and pursued for prosecution.