This release has a potential clearnet leak for Tor users; see 0.4.1 release notes for details. Previous or later versions don't have this. TLDR, don't use this version, but you may need to read the release notes when upgrading.
See release notes at https://github.com/JoinMarket-Org/joinmarket-clientserver/blob/master/docs/release-notes/release-notes-0.4.0.md
Please do read those notes! : in particular, in the Upgrade section, it guides you through the few (not disruptive) changes that you need to make to your Joinmarket setup. As noted in the title, these are not breaking changes, nor are there any security bugfixes, so the upgrade is not urgent (but highly recommended for fixes to various suboptimal behaviours).
Main change areas are: wallet upgrade (big improvements, but no annoying transactions or rescans needed), change to offer selection to increase quality/frequence of success of joins, upgrade for Core 0.17 (deprecates accounts feature).