Surf ramps require extra inward rotation to initiate sliding. Most surf maps are likely broken.
Steps to Reproduce
Place a Canvas Wedge down and scale it up. Rotate the wedge 0.5 degrees forward or backward. Jump onto the ramp and strafe into the ramp.
You can also reproduce this in the surf_beginner Condo Workshop map.
It seems rotating the wedge an additional 15 degrees inwards to create more slope allows surfing again, but this would require rebuilding any existing maps.
What I expected to happen
The player should slide along the ramp.
What happened
The player walks on the ramp.