Wireshark – TCP previous segment lost

Hi,

I was wandering if anyone came across the same TCP traffic behaviour. I have filtered my packet captures on specific TCP conversation and after downloading it into Wireshark can see following:
There are some lost packets which are followed by ‘TCP previous segment lost packets’ (TCP packet arrives with a sequence number greater than the “next expected sequence number’) however they are never retransmitted.
The peer doesn’t send either TCP duplicated ACKs requesting retransmission of the lost packets.
I believed that in TCP connection needs to ACK every single packets and lost packet will always be retransmitted.
Could anyone please advise.

Thanks,

Anna