Attachment only has Assembly, needs all Parts to be able to open.
I guess one of the legs is not straight - make sure to double check the constrains to make sure they are correct
Roll back every part and select planes or sketches that "Should" be parallel and measure each way, one or more of the parts aren't parallel. Did you select a face from a part that isn't parallel, was the part built in context of another part and that part was tilted? This can be a fun exercise to trouble shoot....
I don't know what's the system tolerance or deviation allowed for mate in assembly
Your Leg S2 angle is not the same on both axis
One is measuring 2.8624 and other is measuring 2.8660 and it is repeated on all four legs
This might be the reason to get the error when you try to mate S2 holes
Check your Leg S2 model or Top leg and see if there is any issue