This seems to me as related to Sean Pringle's comments on slow queries (as Dan Andreescu had foreseen :]).
These 3 queries hit a view (defined in config.yaml) named "edits_web".
This view gathers all data from all MobileWebEditing schema revisions.
Currently this sums up to ~100M records.
After that, some filters are applied, which do not take advantage of the table's indexes.
So the query is extremely slow, and getting slower with each new event being inserted.
This report is calculated with timeboxed=false option, so it is calculated from scratch every day.
My guess is that some days it is taking too long and the generate.py can not compute it.