NOTE:
Ahrefs (like most SEO tools) doesn’t recrawl volumes daily. They pull volumes from external clickstream + Google Keyword Planner data and smooth it into an average monthly volume across the last 12 months.
However, if a keyword’s traffic potential goes near zero (because hardly anyone is searching and Google stops showing a distinct SERP for it), Ahrefs may drop it from their keyword index temporarily, or only update it less often.
That’s why you sometimes see keywords “fall out” in off-season periods.