Steps to reproduce:
1. Open the attached project (frustumcullingtextmesh.zip)
2. Open the Assets/main.unity scene
3. Press play
4. You will see the yellow bounds are a line running through each character rather than a box

Note:
Font is custom, everything works fine with the default font

Expected result: Should be rendered a box
Actual result: It appears as a line

Reproduced with: 5.3.7p3, 5.4.4p2, 5.5.0f3, 5.5.1p2, 5.6.0b6