The calls to JoinMulticastGroup and LeaveMulticastGroup on FSocket do not allow for the interface address to be passed in, only the the group address. The interface address is currently hard-coded to INADDR_ANY, which may not select the correct interface in a multiple adapter setup.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-60860 in the post.
| 0 | 
| Component | UE - Networking | 
|---|---|
| Affects Versions | 4.19 | 
| Created | Jun 20, 2018 | 
|---|---|
| Resolved | Aug 18, 2021 | 
| Updated | Aug 18, 2021 |