Hey CrazySiberianScientist,
Try having a look at your Collision Mip Level as well as your Collision Thickness within the details panel of your selected Landscape.
**Collision Mip Level **- Landscape LOD’s to use for collision tests. Higher numbers use less memory and process faster, but are less accurate.
Collision Thickness - Thickness of collision surface, in unreal units.
I hope these suggestions work for you, but if you are still having some trouble try creating an AnswerHub post so we can help you troubleshoot the issue further. Making AnswerHub posts is beneficial to the community as well since others might come across the same issue as yourself and need some help.
Cheers,