I recently noticed that some old search queries of mine (from 2015 or earlier) are broken since the switch to the new search server. One example is the following, which contains a partial date and used to work flawlessly:

https://musicbrainz.org/search?query=begin%3A1%3F%3F%3F-01-01+AND+type%3Agroup&type=artist&limit=100&method=advanced

Also, when a precise date (yyyy-mm-dd) is provided, the results include all entries matching yyyy:

https://musicbrainz.org/search?query=begin%3A1999-01-01+AND+type%3Agroup&type=artist&limit=100&method=advanced