You might face a problem with your system where an even or odd sequence of tills is having issues. You try to reboot the tills and they reboot fine but won't load up the sales screen and you're stuck on the oracle screen with the loading symbol. And this causes your other tills to slow down during testing where you can log into the sales page but once an item is scanned, the tills stop working.
In order to fix this issue, you will have to reboot the server for all the tills, both odd and even-numbered, and reboot all the tills on the shop floor. This should fix the issue.
If you perform the above steps and the tills are still facing issues and are not working correctly, raise a support ticket and the Prologic support team will look deeper into the issue and resolve it for you.