I have done some work with garlic, but have only sporadically seen this physiological disorder.  Plant pathologists confirm that it is not microbial in origin.   Attached is a summary that I recently wrote (which was based on my observations and those of others who have worked with garlic--you can see we are deliberately vague).   

 Waxy breakdown is a physiological disorder that affects garlic during latter stages of growth and may be associated with periods of high temperature near harvest.   Early symptoms are small, light yellow areas in the clove flesh which darken to yellow or amber with time.  Finally the clove is translucent, sticky and waxy, but the outer dry skins are not usually affected.  Waxy breakdown is commonly found in stored and shipped garlic and rarely in the field.  In addition to its association with high preharvest temperatures and sunscald, low oxygen and inadequate ventilation during handling and storage are also reported to contribute to the development of this disorder.

 I hope this is at least a little helpful.  I did a search for recent literature on waxy garlic disorder, but could not find any new references.

– Marita Cantwell