Right Click > “Open Corner” now produce an overlapping point instead of really opening a corner.
Glyphs 4 (4100)
Can you check your stems in Font Info > Masters?
Yes, the open corner radius depends on the stem settings. Set them to something else than 0 (or delete them).
The zero will be ignored on export, but if another master has values, the interpolation will be very wrong. So having proper stems is important.
That make sense. Thanks!