Hi, the page Special:Statistics lists the number of content pages.
The number is updated twice a month: initSiteStats.php is run at 05:39 UTC on 1st and 15th of each month.
According to configuration, wgArticleCountMethod is set to link for this wiki. That means that a page must contain a wikilink to be included in the content page count. So the number might be lower than you expected.

I don't think there is a bug here.

参考訳 / Translation
Special:Statistics には、コンテンツページの統計が表示されます。
これは月に2回、1日と15日の5時39分(UTC)に更新されます。
設定では、wgArticleCountMethodはリンクに設定されており、コンテンツページ数にカウントされるためにはリンクがないといけません。
ここにバグがあるとは思えません。

I will show the information. I had recorded of the number was 162 articles as of Sep. 1st, now, the number is 46.
The existing page has not many moved and deleted significantly, so I think the value is clearly abnormal.

I remember before this the number of articles was over 100.

It currently looks like "164" to me.