I created a glass vial holder using Tinkercad. Looks great in Cura 4.7.1 in Prepare mode but when I look at the same thing in Preview, the middle of the letters disappear as shown.
Not sure why it turned grey so that might be a clue.
Do you have ‘print thin walls’ enabled? I am not sure of the exact wording for the setting as I do not have Cura in front of me. You may have to make the lettering larger.
Yeah, if stuff vanishes it is usually print thin walls, which fixes it.
Also make sure the letters of the model are solid and in contact with the surface. Especially thingiverse models have sometimes issues in this department.