Earlier quoted context omitted.
> I will take this moment also to mention that "re-implement" isn't exactly right in that they modified the protocol slightly to allow for someone in control of the administration server to change a user's private key without their knowing, so that the admin can decrypt the E2E communications using the known key. Do you have a source for that claim?
GP is probably referring to this: https://boelter.blog/2016/04/whats-app-retransmission-vulner...
The GP claim is far broader that all E2E communication can be compromised without user awareness permitting ongoing communication between two unaware parties to be monitored.