Thanks, this was worth digging into, and it changed the data.
The half stalls are real, and they're the same events as the dataset stalls. On those days the dataset total goes to zero, with every dataset frozen. On the model side only part of the counters freeze, and it splits by repo age: about 98% of models created before 2022 keep counting (BERT, CLIP, all-MiniLM-L6-v2), while almost no repo from mid-2025 on does. The old giants are what hold the total at half. 20 of the 21 such days are Wednesdays, and snapshot spacing is 24.0 h on all of them, so it's not timing.
08-13 is a counter catching up. On 08-12, 80% of models with 2k+ daily downloads were frozen at exactly zero (bge-small-en-v1.5, bge-m3, chronos-2, MiniMax-H3), while all-MiniLM-L6-v2 kept counting at twice its usual rate. On 08-13, 94% of them were above 1.8x their own median, and the top 20 explain only 30% of the excess. Frozen models do 2–4x the next day, so these downloads are delayed, not lost.
Your pair rule catches most of them but not all. The share of frozen counters also catches stalls that barely dip the total (2025-12-17, 2026-05-12, 2026-09-02), and misses ones where counters crawled instead of stopping. 06-25 and 08-01 have nothing frozen and normal datasets, but every model sits at about 0.5x and then 1.6–1.9x, so they read as a shifted count too. A day is now a stall if any of these holds: total under 0.3x of the median, at least 25% of models with 60K+ monthly downloads frozen, or your pair test (under 0.7x, made up by a neighbour to about 2x). Datasets use a 90% frozen bar, since they freeze all at once.
And 2025-05-21 wasn't a spike. On 05-19 and 05-20, dl_all went down for 16–19% of models and came back days later. We clipped the drop but counted the rebound: 440M phantom downloads. The same happened from 2026-06-13, another 537M. Snapshots during a rollback are now set aside, and downloads are measured across them.
It's live. The model side has 27 windows and skip_days went from 20 to 59 (datasets 57 to 65). The Hub total dropped 0.99B to 43.48B, all of it from the two rollbacks, and days outside 0.7–1.3x of the median went from 70 to 40. 08-01/02 is the one pair that still slips through, right at the edge of the sum band.
