System Information
Operating system: Darwin-19.6.0-x86_64-i386-64bit 64 Bits
Graphics card: AMD Radeon Pro Vega 48 OpenGL Engine ATI Technologies Inc. 4.1 ATI-3.10.18

Blender Version
Broken: version: 2.91.0 Alpha, branch: master, commit date: 2020-09-10 21:55, hash: rB66078594d130
Worked: (newest version of Blender that worked as expected)

Short description of error
[Please fill out a short description of the error here]

Exact steps for others to reproduce the error
[Please describe the exact steps needed to reproduce the issue]
[Based on the default startup or an attached .blend file (as simple as possible)]

Using Sculpt for the first time I wanted to Mirror the Eye2 object. No matter what I did, there is no way the object would mirror other than tight around its own origin for X or Z and Y was unrelated to any axis. It seemed to be locked around something like Local Transform.with the Origin in Geometry center. I looked around Object mode and noticed View / Local View / Remove from Local View. My Eye has been removed from Modeling mode and can't be retrieved with Undo. The Eye still appears however in Layout and Sculpt mode but can't be selected except in the Collection listing. I tried selecting it and Snap to Cursor to no avail. Now my horse has lost its only Eye!
This is a minor problem compared with not getting Mirror to act as expected.

Latest build 051020 (d,m,y) fixes the problem.