These are the changes of ARK: Survival Evolved’s Patch 185.5, grouped into categories for clarity. If not otherwise indicated, they’re quoted from the relevant Steam Thread.

Official Servers

• Official Servers Upgraded to Difficulty 3.0.

Bugfixes

• Unversioned Hotfix: Fixed a Client startup crash, Fixed Linux Server startup crash
• About +30% server performance gain
• Fixed the fix: Max height of structures above the ground is now 25,000 units. Previously was 15,000 units.

(Original Announcement on Steam)

Here are the patchnotes of the previous patch (185.4)