You have to recalculate the adaptive op, otherwise the file would be too big.
You have to add the edges from part and stock in two passes. If you select edges from stock and part during op creation you get an error message like "use only edges from one part". Follow this advice, create the op, reopen the "basic geometry" section and add now the three edges from the stock. Here I visualize the selected edges for this op. Again, these "nearly closed" edge loops work only with adaptive op.
OS: KDE neon User Edition 5.17 (KDE//usr/share/xsessions/plasma)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.18614 (Git) AppImage
Build type: Release
Python version: 3.7.3
Qt version: 5.12.5
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: German/Germany (de_DE)