Assert "already tessellating!" when completing a race in Extreme Speed Runner

Partner Rank: 4

Verification build: 1.15.0.51 3706814

Summary: Assert "already tessellating!" when completing a race in Extreme Speed Runner

Impact: Asserts are bad and can result in failures during cert and content review if they're not caught and logged. While there is no apparent gameplay impact, it's clear there is something going wrong under the hood.

Repro:

1. Download Extreme Speed Runner from the store.
2. Create a new world with the Extreme Speed Runner template.
3. talk to the npc
4. begin a race (any)
5. complete the race

Observed result: Assert shown

Expected result: No assert
Screenshots attached: Yes, above