Hi Sourabh,
It certainly seems to be an off-behavior. I would suggest take a look at the different words/terms which have come as an update from your service provider.
Assuming you haven't changed any of the SPL settings in a while, here are a couple of things I would suggest:
1. Check if you have subscribed to any new list type Eg: IRAN list type got activated on April 6 from US authorities which has got generic names more like single terms
2. Check the SPL file the day you found blocks or the prior day to assess how many updates came in on the file and assess the updates.
Highlight some examples for us to give further suggestions.
Hope it helps!
-Shrini