What may be causing this "tile" effect on navmesh?

Hello @Ares9323 ,
You could try the following.
First, increase the Tile Size UU. Another thing you can try is adjusting the Cell Size and Cell Height values. In many cases, tweaking these settings helps resolve NavMesh generation issues like the one shown in your screenshot.

Then rebuild the NavMesh by going to Build - Build Paths.

I’ll also leave a few posts below that mention the solutions I described above, as they might be helpful for reference.

Hope it helps!