There are no known security issues with "Siacs OMEMO" / OMEMO v0.3¹ despite of what some very loud Signal fans would like you to believe. It has been audited by a third party² who took a longer look at it than all of the Signal fans combined.
Yes, #OMEMO v0.7+ (or TWOMEMO 😜) is a cleaner spec with more features (most notably Stanza Content Encryption). That’s why we wrote it. I’m a co-author. That doesn’t mean v0.3 is insecure.
¹: https://xmpp.org/extensions/attic/xep-0384-0.3.0.html
²: https://conversations.im/omemo/audit.pdf
#XMPP
OMEMO Encryption
This specification defines a protocol for end-to-end encryption in one-on-one chats that may have multiple clients per account.Andreas Straub