Reproduction steps:
1. Open attached project "1316145.zip"
2. Open "MainScene" in the Scenes folder
3. Open Tile Palette in the Top-Menu/Window/2D
4. Enter Play Mode
5. Observe the Tiles in Game View

Expected result: Diagonal lines in Tiles look sharp, same as in the Tile Palette
Actual result: Diagonal lines in Tiles look distorted (some have more noticeable waves and distortions than others), not the same as in the Tile Palette

Reproducible with: using 2D Tilemap Editor 1.0.0 (2019.4.21f1, 2020.2.6f1, 2021.1.0b8, 2021.2.0a6)
Couldn't test with: 2018.4 (as the 2D Tilemap Editor package is not available)

Note: You can additionally paint more Tiles with diagonal lines while in Play Mode using Tile Palette, to see more distortions (using the Scene View)