> QUESTION: My old SSS materials appear black, what should I do?

Check the attenuation distance on the BSDF with SSS, it is probably too low. You will also see that this control is locked. To unlock it and change it, please remove the SSS layer, change the attenuation distance and remake the SSS layer.
This could be happening with materials that include SSS that were made before Maxwell Render version 1.5.

> PROBLEM: Glass objects come out black

Check your transmittance color and attenuation distance. The attenuation distance should be around 3cm for common glass and about 40cm for high grade glass, of course you must check your scene scale too.  Also make sure your transmittance color is set to anything other than pure black (0,0,0).