Host machine stacks up large amounts of Sockets in "CLOSING" state

I recently noticed an increase in CPU on our otherwise low CPU util MaxScale proxy.

MaxScale is logging many hundreds of the following error:

Failed to connect backend server [host]:port due to: 99, Cannot assign requested address.

Checking out local sockets

$ ss -tanp | awk '

' | sort | uniq -c
3 CLOSE-WAIT
43934 CLOSING
1307 ESTAB
5848 LAST-ACK
48 LISTEN
1 State
9695 TIME-WAIT

The issue has only just recently appeared in the last 2 months, so uncertain to as what may have changed.