Contractions or what...

I woke up today having time-able contractions, 6-8 minutes apart, and more uncomfortable than usual BH. I had an appointment and ended up needing a stress test, and then I was sent to labor and delivery for more testing. Everything was okay with baby but none of my contractions showed on either stress tests? I’m clearly having them, my stomach gets rock hard and I get uncomfortable. This is my fourth so I’m aware what they feel like. Has anyone had this happen? I just don’t understand how they weren’t showing up at all.