We are also having this issue. Shopify support told us the following:
To troubleshoot the issue with the POS app only showing ten products, you can try the following steps: confirm that the app and device are up-to-date, check app permissions, reset the account, reset the Bluetooth connection, reinstall the app, and reset the network connection.
None of these steps have worked and we can not reset our account as that would entail fully starting over. We have a big sale coming up and need to see more than ten products at checkout to double check our items, or remove an item if a customer changes their mind. Shopify PLEASE fix this, it’s a huge headache for our staff.