When TNT is lit, it's supposed to hop in a random direction (as evidenced by the fact that it hops in any direction at all, and observed behavior in the Java edition of the game). However, when TNT is lit or fired from a dispenser, it always hops the same distance in the north direction.

To reproduce, simply go into a creative world and light multiple TNT at once (doesn't matter if you use Flint and Steel or Redstone), and they will all jump in the same direction (north). You can also observe this happening if you fire TNT out of a dispenser at any angle.

To study the problem deeper, I used /tp ~~~ 0 (which sets the player's yRot value to 0) and it makes you face north, the same direction that TNT always hops in. This means that the game considers North to be the direction associated with an angle of 0. This implies that the issue with TNT is simply some missing or broken randomizer code that returns 0 instead of a random number between 0 and 365 when the TNT asks for a direction to jump in. Hopefully, this insight is helpful for a quick and easy fix to this issue.