(Addresses and ports randomly made up for the sake of example)
Suppose we have a machine and it's private IP address is 192.168.1.10.
Suppose the machine's router's public internet IP address is 18.104.22.168.
The machine sends a UDP packet from port 7000 across the internet to some address at port 9000.
This could be translated to: src: 192.168.1.10:7000 -> src: 22.214.171.124:37500
After this, but before the NAT record above is cleaned up, the machine sends a TCP packet from port 7000 again to a different address at port 9500. Will the router translate port 7000 to port 37500 again, or will it randomly choose something else?
I would take the guess that it would use that same port number (37500), because it's important have as many available ports as possible for other machines connected to the router to use.