I realized that every time I go to the add/remove materials section for my vocab list, and select to add terms individually, there are almost 100 words being removed from my study schedule under "Removed from list".
I noticed this as there were some common words not showing up in my schedule like 風/かぜ. It turned out this among others was in this long list of terms being removed every time I updated my vocabulary materials. Every time I go in to add/remove materials, this list fully populates again with "Removed from list" terms i.e. I can't update my materials and click save without having to go in and add all these terms one by one again.
I assumed this might be part of the duplicate/standard reading wipe recently, but given basic terms like 風/かぜ I wondered if this was the case.