i have not experienced this particular problem however, with pipes , it seems that on occasions, it depends on how you construct and edit your network.
For instance, i coded in some pipes and structures and then deleted a pipe and a structure, added two more, connected them up. modified the underlying alignment to suit.....and from that point on, I could not add labels to my profile view for that pipe alignment.
I deleted that part of the network and coded it in again by adding pipes and structures first, then using the "Create alignment from network parts" command to make the alignment and the profile view (it was quite small)..... and from then everything went fine.
I suggest that if you are on Subscription (and why should't you be!), make use of the AutoDESK Support Team available to you and log this with them....they will respond.
cheers,
Peter T.