Please check the page in "learnOSM" below too. (Japanese)
"learnOSM" 内の「編集テクニック: よくある間違い」も参照してもらうといいと思います。
https://learnosm.org/ja/josm/josm-editing-techniques/?search=mistake#%E3%82%AA%E3%83%96%E3%82%B8%E3%82%A7%E3%82%AF%E3%83%88%E3%81%AE%E6%8E%A5%E7%B6%9A

...and OSM wiki
osm.wiki/JA:%E7%B7%A8%E9%9B%86%E3%81%AE%E6%A8%99%E6%BA%96%E3%81%A8%E6%85%A3%E4%BE%8B#.E3.82.A8.E3.83.AA.E3.82.A2.E3.81.A8.E3.82.A6.E3.82.A7.E3.82.A4.E3.81.AE.E3.83.8E.E3.83.BC.E3.83.89.E3.81.AE.E5.85.B1.E6.9C.89

Hello! Thank you for mapping around Gifu prefecture.
I'm afraid to say, I found some mistakes in your mapping.

1. Connecting the node constructing roads and other node constructing buildings or areas is not appropriate. Please disconnect their nodes.

2. The polygon which has "building=yes" tag must surround just building boundaries, not building site.

Thank you for your cooperation.

Thank you for your comment and advice!
コメントありがとうございました. 次に編集する時に気をつけます/修正します.