These are all Community ♦ bumps, separated by exactly one hour (They occur on
hour:38:16 UTC). Could the bot be sedated please? We're a 4-questions-per-day site; a bump an hour is not good for business.
We used to have one bump per day. This is evident if you scroll down on the homepage and check the timestamps (screenshot).
Apparently the number of questions bumped per hour is a configuration value. Maybe this got tweaked?