These are the changes of ARK: Survival Evolved’s Patch 204.1, grouped into categories for clarity. If not otherwise indicated, they’re quoted from the relevant Steam Thread.

Bugfixes

• Fixed bug that was detaching carried Monkey on clients
• Fixed randomish missing mod engrams
• Fixed overspawning plesios in mods
• Fixed (likely) bug that was causing some players to be invisible for the host on non-dedicated sessions

(Original Announcement on Steam)

Here are the patchnotes of the previous patch (204.1)