On my listens page, I noticed that many of the tracks I had imported from last.fm were linked to "recordings" like http://musicbrainz.org/recording/87b4b400-63e1-31d8-9e99-b8f6b3e35ed9 - but that's actually a track mbid and the correct link is https://musicbrainz.org/track/87b4b400-63e1-31d8-9e99-b8f6b3e35ed9

It looks like the issue is that in new scrobbles, last.fm inserts a track mbid determined using its own matching (replacing the recording mbid if they got a match!). For example, here's the same scrobble from libre.fm (which returns the data exactly as submitted):

<track>
<artist mbid="">L連.NET</artist>
<name>ペロ…これは毒キノコ？</name>
<mbid/>
<album mbid="">幻想マインドブラスト</album>
<url>https://libre.fm/artist/L%E9%80%A3.NET/album/%E5%B9%BB%E6%83%B3%E3%83%9E%E3%82%A4%E3%83%B3%E3%83%89%E3%83%96%E3%83%A9%E3%82%B9%E3%83%88/track/%E3%83%9A%E3%83%AD%E2%80%A6%E3%81%93%E3%82%8C%E3%81%AF%E6%AF%92%E3%82%AD%E3%83%8E%E3%82%B3%EF%BC%9F</url>
<date uts="1552235403">10 Mar 2019 16:30 GMT</date>
</track>

and from last.fm:

<track>
<artist mbid="">L連.NET</artist>
<name>ペロ…これは毒キノコ？</name>
<mbid>87b4b400-63e1-31d8-9e99-b8f6b3e35ed9</mbid>
<album mbid="21440c13-fd9c-474b-a70e-d75516f963b1">幻想マインドブラスト</album>
<url>https://www.last.fm/music/L%E9%80%A3.NET/_/%E3%83%9A%E3%83%AD%E2%80%A6%E3%81%93%E3%82%8C%E3%81%AF%E6%AF%92%E3%82%AD%E3%83%8E%E3%82%B3%EF%BC%9F</url>
<date uts="1552235403">10 Mar 2019, 16:30</date>
</track>

And here's an example for a scrobble that included a recording mbid from libre.fm:

<track>
<artist mbid="">メロキュア</artist>
<name>Sunday Sundae</name>
<mbid>6f8a308f-28fd-4072-8153-2569b09b2d26</mbid>
<album mbid="">メロディック・スーパー・ハード・キュア</album>
<url>https://libre.fm/artist/%E3%83%A1%E3%83%AD%E3%82%AD%E3%83%A5%E3%82%A2/album/%E3%83%A1%E3%83%AD%E3%83%87%E3%82%A3%E3%83%83%E3%82%AF%E3%83%BB%E3%82%B9%E3%83%BC%E3%83%91%E3%83%BC%E3%83%BB%E3%83%8F%E3%83%BC%E3%83%89%E3%83%BB%E3%82%AD%E3%83%A5%E3%82%A2/track/Sunday+Sundae</url>
<date uts="1552237259">10 Mar 2019 17:00 GMT</date>
</track>

And from last.fm (note that the mbid got replaced!):

<track>
<artist mbid="aee987d8-46a2-47f0-b958-ff9d0ff8b305">メロキュア</artist>
<name>Sunday Sundae</name>
<streamable>0</streamable>
<mbid>185e6290-bf5c-48fa-9544-d75f433bf4c6</mbid>
<album mbid="">メロディック・スーパー・ハード・キュア</album>
<url>https://www.last.fm/music/%E3%83%A1%E3%83%AD%E3%82%AD%E3%83%A5%E3%82%A2/_/Sunday+Sundae</url>
<date uts="1552237259">10 Mar 2019, 17:00</date>
</track>