I’ve decided to test a “new” steam report related to the journey steps obtain a mount and animal companion. On Siptah release (15.09), I was able to complete them both without any issue by placing a single horse but it seems that some of the subsequent patches broke them or they don’t trigger consistently. I started a new char in single-player (fresh database, no mods, exiled lands map), placed a bunch of horses, rhinos and various animals but I was not able to trigger the journey steps.
If the other reports are any indication, the issue my have been introduced by hotfix 2.0.1 or 2.0.2: