CC folder collaborators were erased, when I add them again, then log in to see the invitations, they disappear again

Yesterday all the collaborators from a CC folder project were errased. After that I send them invitations again in order to re-incorporate them. After a while I logged to my CC and under the collaborators tab from that folder project no invitation were display.

What may be happening? Everything was working ok, for about 2 weeks.

Thanks Anyone.