If water conditions are OK, which they seem to be as I can see other zoa's opened up in pic., then I would say new ones are just getting acclimated to new conditions...
Most common zoa predator that often show up with new colonies are Sundial snails...
My zoas were slowly being decimated till I found a couple of these.
They are real hard to see hunkered down in polyps or hiding nearby till night, when they go out and wreck havoc on your beautiful zoa colonies.
Look closely..
If none about, would consider some serious back to back water changes to dilute any possible toxin build up in tank...
Good Luck!
Keep us posted.