The activity feed on Competitor Tracking lists what your tracked channels did since their last sync, newest first.
New video
The channel published a video.
View spike
One of the channel's videos crossed a view milestone. The milestones are 1,000, 10,000, 100,000, 1,000,000, and 10,000,000 views.
Upload cadence changed
The channel's upload pace moved. YTNiches takes its average uploads per week over the last 4 weeks. If that average moves by at least 1 upload per week between syncs, it shows up here.
Outliers
When one of the channel's videos becomes an outlier, it lands in the feed too. What an outlier is explains the rule.
How fresh is it?
As fresh as the last sync. See How often channels sync.
How long it's kept
Feed items stay for 30 days. YouTube only lets us keep its data that long, so older items are deleted.