Hi, 
I use Acrobits (ios and android) and Freeswitch with ZRTP (MiTM). 
During call acrobits show an error: "The PBX is offering an enrollment, but you are already enrolled. Don`t Trust PBX". 

In freeswitch log: 
[DEBUG] switch_rtp.c:1370 [zrtp protoco]: INFO! User have been already registered - skip enrollment ritual. ID=1008 
[DEBUG] switch_rtp.c:1327 User already enrolled! 

Please help