The ack is the acknowledgement of the receipt of all previous (data)-bytes sent by the other side of the TCP-connection.

In most occasions every packet of a TCP connection has an ACK flag after the first SYN and a ack-number which increases with the receipt of every new data-byte.

Here, that ack-number sequence is not an incremental of the previous ack-number.

#SURICATA STREAM TIMEWAIT ACK with wrong seq
suppress gen_id 1, sig_id 2210042