Hi Annonaceae,
I grow these fragile species + some subincanum in the conservatory and after 5 years of contact with them I estimate that I am still a beginner. Usually it may be a matter of the local microclimate, insects or too young age or to small size of individual species (from what you are writing, these last two things look unlikely for your plants).
If you can ask directly, more experienced people:
about grandiflorum: Bryan, Montoso gardens from Puerto Rico
about bicolor: Micah from Hawaii
about gileri: Jim West from Ecuador
Only Micah is often in this forum, the rest must be asked personally by email.
Regards
Dominik