Platformer - Getting stuck on 45 degree slopes from standstill

I'm prototyping a platformer using Tilemap for stages.

If the player is running at max speed (about 720pps), they can walk up 45 degree slopes just fine. But if they are already standing stationary on a slope and start running up, the player inches up a few pixels then stops. Debugger shows the X vector around 240pps.

Any way to fix this?