UI began showing 0 pageviews, but a usual number of visits

All of a sudden, starting from 25th July in all reports I see 0 pageviews, but a usual number of visits, events and goals. “Pages” section also does not show any URLs.
Previous time data is not affected. Middle of 24th has half of usual pageviews, I guess, in the middle of day something had happened. Absolutely nothing was done on the server of Piwik files at that time…

Piwik version is 2.16.5. This installation has 100s of sites. It also uses queued tracking - it seems to work properly, monitoring shows incrementing values, and they decrement when queue processing runs.
Archiving seems to run fine - archiving log shows that archiving process sees visits of sites.

What can be the cause of missing pageviews and presense of visits?