Other walls on layers not visible that have higher intersection priorities!
And if those walls need to be in the hidden layer, then you can change the intersections priority number of the layers themselves (in the layer settings dialogue) so that the visible and hidden layer have different IP numbers.
Then they won't intersect with each other.
remember the IP numbers get save with the layer combination so you can have walls in one layer combination intersect and in another they won't.
One of the forum moderators.
Versions 6.5 to 25
Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10
Dell Precision 3510 - i7 6820HQ @ 2.70GHz, 16GB RAM, AMD FirePro W5130M, Windows 10