Repro steps:
1. Open attached project
2. Build and run on Android/iOS
3. Choose "Augmented Reality" and then "Use default settings"
4. Scan a plane and when one is detected press on it to spawn the UI
5. Press OK

Actual: Text is shown as white rects or doesn't show up at all

Reproducible with: 2019.4.4f1 - TMPro 2.1.0

Tested and reproduced on these devices:
VLNQA00294, Oppo Reno Z 中国版 (PCDM10), Android 9, CPU: Mediatek MT6779 Helio P90, GPU: PowerVR Rogue GM9446
VLNQA00001, Google Pixel 2 (Pixel 2), Android 11, CPU: Snapdragon 835 MSM8998, GPU: Adreno (TM) 540
VLNQA00128, Samsung Galaxy Note8 (SM-N950F), Android 9, CPU: Exynos 9 Octa 8895, GPU: Mali-G71
iPhone 11 (iOS 13.5)

Notes:
- On iOS no text is shown at all