Hi Jiri, I have the same issue.
I think it is not a performance degradation but I think that root cause in skipped messages. For example, frame 56 in your debian10_sctp_test_to_sctp_test.pcapng shows that the data message with sctp.data_tsn == 919935042 was received on server interface but it was acked in frame 78 only. It happens periodically with high-load traffic. The server can capture DATA on network interface but SCTP level does not receive it. Best regards, Evgeny