I just came across the same thing and found that this was happening after a SYN packet didn’t reach its destination.
So “Spurious Retransmission” doesn’t always mean it’s a “needless transmission”.
In my case, there was a firewall denying it.
Source sent SYN, destination was expecting it but didn’t receive so it sent a [RST, ACK].
Then the next SYN attempt showed up as TCP Spurious Retransmission.
Then went back and forth until the client gave up.