What you may be experiencing:

Merchants are reporting error "POS got stuck for a second and needs to be closed.." , after updating QuickBooks Point of Sale v12 to R13 or v18 R3.

Current Status:

Great News! This is now resolved with the latest Point of Sale versions of 2012 Release 14 & 2018 Release 4. You can download the manual patch within the following article: https://support.quickbooks.intuit.com/Support/ProductUpdates.aspx