Don't expect corners to be spotless.

Yes, it’s normal, and no, you probably can’t fix it completely.

Robot vacuums are round. Corners are square. That geometry means the brush can’t reach all the way into the corner. The side brush helps, but it just kicks dirt around. Some of it ends up in the corner anyway.

You can tweak settings: increase cleaning passes, turn on edge mode, or run it more often. That helps, but doesn’t solve it. Models with a D-shape or better corner-cleaning brushes do a slightly better job, but none are perfect.

If it really bothers you, grab a stick vac once a week and hit the corners in thirty seconds.

A robot vacuum does 90% of the work. The last 10% is yours.