We digged into it further and found out that our projectiles initial location direction was wrong.
The reason why the physics where so framerate dependent is tricky;
Our projectiles are shot from canons;
The projectile start position initial transform rotation was wrong by 90 degrees. As a result the projectile bounced inside the canon but somehow managed to shoot out straight out of the barrel making us think everything was fine…
We rotated the transform and now the projectiles paths look similar on both low and high end computers.
Basically this confirms that physics are fine for projectiles, but don’t rely on bounces. This said if you need to make something bounce just a couple of times I suppose it should be fine.