I got a nanosuit jammer in Capture the Relay, then when I used it the message didn't go away. So I could press P again and it would say "Nanosuit jammer already active!"
Then the next round started and I could use it again.

Don't think it's a bug - AFAIK your team can only put one down at a time. If another member of your team has one down you can't place yours. I could be wrong though.

That's right. Only 1 jammer at a time.

No, the thing is, I deployed it but the "Nanosuit jammer available, press P" message stayed there and the next round I got to use it again for free