How to reproduce:
1. Open the attached "TestFor1068658.zip" project
2. Play the Scene and observe the Labels displayed
3. Go to to Fonts folder in the Project view and Select Test Font
4. Change Character set to any of the ASCII sets in the Inspector window
5. Play the Scene again
6. Notice that some of the Labels disappeared

Expected result: Labels are visible when transformed with GUI matrix
Actual result: Labels disappear when transformed with GUI matrix

Reproducible with: 2017.1.0a1, 2017.1.5f1, 2017.2.3p3, 2017.4.9f1, 2018.1.9f1, 2018.2.3f1, 2018.3.0a8
Not reproducible with: 5.6.6f2

Note: from 2017.1.0a1 to 2017.1.0b6 versions only scaled Labels disappear, from 2017.1.0b7 version and up all transformed Labels disappear

Update: fixed in 2018.3.0b9, 2019.1.0a6