You are probably using some type of heater hose and the oil is going right through it. I had the same problem when I installed a UPR can on my 14 GT. I didn't use the supplied hose because it was half collapsed so I went to the parts store and bought some heater hose not realizing it was not suitable for oil.
I later had to go back and get some PCV/emissions type hose and didn't have anymore problems.
2014 GT, Automatic, Sterling Gray metallic, GT500 AB. Ford STB and aluminum diff cover. Bob's oil catch can.