I'm trying an animation in Blender 2.8 (most current release as of 20 Jun 19, although the last couple of releases also do this) which fades up pre-extruded text part way through; I'm running Transparent BSDF and Principled BSDF* nodes through a Mixer node and keyframing the Mixer fac setting to adjust transparency. The text is extruded using the Text Geometry Extrude setting.
Using Eevee, I'm finding that, while the extruded sides of the text are fine, the front face is missing; when viewed from the reverse, the rear face is missing, however Fill Mode is set to Both. The effect is not present in Cycles. (No, I don't want to wait for 160-odd frames to render under Cycles!)
Any ideas, please, if this is a 2.8/Eevee problem and/or if there is a way to get around the difficulty? (Apart from rendering in Cycles, of course).
*Diffuse BSDF also has the same problem.