There are 3 types of streamer issues in the Cisco Firepower FMC and in different releases.
The first is the enforcement of TLS, which was introduced in 6.1. That broke the most integrations.
The second issue is eStreamer documentation requires a two-way SSL authentication. At some point, the client part of authentication started failing because of a bug.
The third issue is connected to how NetAMP works on FirePower. The short of this problem is the integration is not fully baked.
You can access the eStreamer information from System>Integration>eStreamer:
Supposedly, there is a fix coming out this week or next, but Cisco has planned to depreciate eStreamer in interactions over the next 24 months in favor of a syslog protocol.