Use "C-Shift-P MonkeyC: New Project" to create a new DataField app, "C-Shift-P MonkeyC: Edit Products" to add your favorite devices, then build with Strict type checking. It fails to build with:
ERROR: fenix5xplus: DataFieldTest/source/DataFieldTestView.mc:40,12: Cannot find symbol ':locY' on type 'Null'.
ERROR: fenix5xplus: DataFieldTest/source/DataFieldTestView.mc:42,12: Cannot find symbol ':locY' on type 'Null'.
Confirmed with 4.1.7 and 4.2.1
(and yes, obviously I know how to fix it - I'm reporting it so that Garmin can fix their templates)