2D Tileset - Graphical artifacts/glitches - How can I solve this?

I have been making a top-down game and created my own tileset.

When I am playing the game some glitches appear on the map. I already tried to use the condition tile sheet texture but the glitches appear there as well.

It looks like this: https://www.reddit.com/r/unrealengine/comments/rvqulp/2d_tileset_showing_grid_lines_while_playing_how/?utm_source=share&utm_medium=web2x&context=3

Is this a bug or how can I fix it?