During the year, I have rolled up to several of the Dynamics NAV 2018 cumulative upgrades implementing new functionalities and unfortunately also fixed multiple errors in the standard application.
Upgrading to Dynamics NAV 2018 CU 5: the sales lines started to give the error: Another user has changed the sales line. Just entering the Line Type, The Item No. and the Unit of Measure code. Therefore, entering a line you needed to leave the document window and reenter to continue.