Downloads from maven.mozilla.org take forever when going over IPv6

I noticed downloading from maven.mozilla.org (e.g., https://maven.mozilla.org/maven2/org/mozilla/telemetry/glean-native-forUnitTests/60.1.1/glean-native-forUnitTests-60.1.1.pom) in tb-build-03.torproject.org takes forever. But I also noticed that if I force wget to use IPv4, the download is immediate.

This is noticeable also when pinging the same host: IPv6 sometimes has 100% packet loss, whereas ping with IPv4 has 10.3 ms of latency.