Please read the release notes at https://github.com/JoinMarket-Org/joinmarket-clientserver/blob/master/docs/release-notes/release-notes-0.9.9.md for details on what this release includes.
( Edit 31 January: there was a brief period where github changed the compressed tar.gz source code archive file; it has been verified that the source code was not in any way tampered with, but if you downloaded during this period, you will find the signature on the .tar.gz will not verify. In that case you can simply download again )
This release includes some needed changes to address issues with Tor connections, and for this reason principally, all users should upgrade as soon as possible, and should also recreate their joinmarket.cfg file.
This release also includes corrections to transaction fee estimation for non-standard output types, fixes to sendpayment, and corrections to a few minor bugs.
The release now also includes OTS timestamp files of the gpg signatures provided, that can be verified using the opentimestamps client.