I have been reporting through Feedback Assistant almost daily our Mac Studio's panic at Shutdown since 14.1 betas started. If the Mac is shut down at the login screen or immediately after logging in, it will execute a normal shutdown. If used for any length of time beyond that, it will panic at shutdown and reboot.

Hardware: • Mac Studio (M1 Ultra) • Apple Silicon • Sufficient free disk space (~35GB+ available) • SIP enabled • 4 local Time Machine snapshots present Current System: • Already running macOS Tahoe beta • Attempting upgrade to macOS Tahoe 26.4 Beta (Build 25E5207k) Primary Issue: Software Update downloads successfully, then moves to “Preparing…”. It stalls at “About 5 minutes remaining” for ~10–15 minutes and fails with: “Failed to prepare the software update. Please try again. An error occurred while downloading the selected updates.” The error appears network-related, but download always completes. Observed Behaviour: • “Checking for Updates” completes in <3 minutes. • softwareupdated and mobileassetd CPU usage <1%. • softwareupdate --history shows no record of the failed beta install. • No excessive system load or obvious disk pressure. Steps Already Attempted: 1. Standard Software Update retries • Multiple download/retry cycles from System Settings. • Same Preparing failure every time. 2. Permissions / Disk Access • Granted Terminal Full Disk Access. • SIP remains enabled. • Some system-protected locations still return “Operation not permitted”. 3. Cache / State Cleanup Attempts • Removed /Library/Updates/*. • Cleared temporary softwareupdate folders under /private/var/tmp. • Attempted MobileAsset cache cleanup where permitted. • Killed softwareupdated and mobileassetd processes (auto-restarted by launchd). 4. Beta Channel Reset • Turned Beta Updates OFF in System Settings. • Rebooted. • Re-enabled Beta Updates. • Forced catalog refresh via softwareupdate -l. 5. Snapshot Check • tmutil listlocalsnapshots / shows only 4 snapshots (normal range). 6. Full Installer Workaround softwareupdate --list-full-installers shows: • macOS Tahoe Beta 26.4 (25E5207k) • Tahoe 26.3 / 26.2 / 26.1 • Sequoia / Sonoma / Ventura / Monterey installers Downloaded installer via: softwareupdate –fetch-full-installer –full-installer-version 26.4 Installer downloaded correctly: /Applications/Install macOS Tahoe Beta.app 7. startosinstall Method (Apple Silicon optimized) Attempted install with: sudo “/Applications/Install macOS Tahoe Beta.app/Contents/Resources/startosinstall” –user –agreetolicense –nointeraction –forcequitapps –rebootdelay 30 –passprompt Authorization succeeds, installer begins preparing, but installation still ultimately fails. Additional Notes: • CPU usage remains low during failure. • No excessive snapshot count. • Error messaging consistently references download/network even though download completes. • Issue appears to occur during cryptex/asset preparation phase rather than initial download. Question for Apple / other developers: Has anyone else seen Tahoe 26.4 beta fail specifically during the Preparing phase on Apple Silicon (especially Ultra-class chips)? Looking for confirmation whether this is a known MobileAsset or cryptex staging issue, or if logs indicate a deeper APFS / volume-owner authorization problem.