I've got exactly the same problem!
I used to sync my playlists, tracks and podcasts in Wi-Fi mode without problems
: PC W7 with MMWGold last version <=> Alcatel idol 4 android with MMAGold last version and 128go sd card.
Since two days, some of my playlists appears "empty" and I can't access to some of my podcasts...
I'll try the tip you suggest in your post to resolve this problem. But I don't understand :
-Why this problem appears after a well functioning period?
-How to do with my podcasts?
-If I create a new playlist, do I have to import it manually?
I'm disappointed... I will keep in use my old ipod classic!