The RCV buffer is initialized with the host's Initial Sequence Number value. If the host is the receiver, the ISN of the sender peer has to be used.
The issue results in the "SEQUENCE DISCREPANCY. BREAKING CONNECTION" error report upon the first data packet received.

Before PR #2711 the correct value was set after the RCV buffer had been initialized via CUDT::applyResponseSettings(..).
After the PR the RCV buffer may not yet be created when CUDT::applyResponseSettings(..) is called for the first time.

If it happens to be called once more or if the distance between the host's ISN and peer's ISN is not that big, the sending would work.

SRT versions with the bug: v1.5.2, v1.5.2.rc.2.