Steam sessions are unable to be found in packaged games that use a source built editor from Github. According to users, this is related to the BuildId not being set properly so the packaged games are not able to see each other. This also may be related to the CompatibleChangelist and Changelist field being empty, but that was also the case in 4.19's release.
This can currently be worked around by adding a BuildId override to the following lines to the user's project's defaultengine.ini in the OnlineSubsystem section:
This did not occur in 4.19.2
Note: This has not yet been tested in Main. That is currently being tested.
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-62144 in the post.