Lately there has been a bug with the IG POS terminals, where after a stretch of uptime the receipt printers suddenly stop working and swapping USB ports or pressing reinit printer does not fix.
To resolve this simply log out to the login screen and close the app by pressing the three dots in the top right corner and pressing the power button as can be seen in the image below.
Once the App is closed, press the below desktop icon to reopen. After a minute or two the terminal will be ready for you to login again, and printers should now be working. If they still aren't working, let us know.