To reproduce:
1. Build and run attached project
2. Observe that all text fields in the game render as pink squares

Notes: this only happens in the build. In the scene and game views, everything is fine. It only shows up in the build. The original project is an HTC Vive VR game using the SteamVR plugin. This has all been removed in an attempt to narrow things down. When you open the project, you may have to re-set the player settings to not use VR, so there is still something in unity's files that is referencing this. The text in my file is newly-created. All canvases were originally world space, but creating one in screen space makes no difference. See attached screenshot showing the scene, game, and player views.

Reproducible: 5.5.0b9, 5.6.0a1
Regression from 5.4.2p2