I had bleeding at 34 weeks, was warded and put on the monitor machine thing (think it’s called CTG or something), and similarly it detected regular contractions though I couldn’t feel any. The doctors didn’t mention about short cervical length though. Maybe it was braxton hicks that’s why we couldn’t feel it. As the bleeding stopped, I got discharged, and the doctors advised me to rest and avoid walking/household chores too. They also gave me anti-contractions meds to be taken till week 36.
I brought up this question about “not feeling contractions” in my subsequent consultation with gynae, she said real contractions will definitely be painful, we will definitely feel it, and it will get more intense over time, it won’t go away until baby is out. I’m 38 weeks now and still waiting to feel the real thing :)