Jetpack Stats altered and incorrect

I’ve been using the classic Jetpack stats view ever since I started my site in February, 2015. I’ve never had a problem with Jetpack’s stats before, but noticed on January 2, 2024 that all of the historical traffic data has been altered.

The daily bars on the monthly chart on the Jetpack stats front page still show correct traffic for each day. However, when I click on the “Summaries” button at the upper right corner of the chart, all of the historical figures shown in the Months and Years, Average per Day, and Recent Weeks tables on the next page have been significantly reduced from what they’d always been before. In general, the new numbers run roughly about 1/3 of what they used to be.

I’d taken a screenshot of the “Summaries” page at 8:57 AM on January 1st, 2024 and the data was still correct then.

I’ve noticed that on the Recent Weeks table the current day’s traffic is correct, and agrees with the current day’s traffic shown on the last daily bar of the monthly chart on the Stats front page. However, when I check the next day, this data in the Recent Weeks table has been altered and no longer agrees with the corresponding daily bar on the monthly chart.

I’m running Jetpack 12.9.3, PHP version 8.1, on a Bluehost server. All plugins are up to date. Clearing cache made no difference.