Overview
Recently, I ran into a serious networking issue after upgrading one of my Macs (“Ripley”) to a beta release of macOS.
What initially looked like a minor connectivity problem quickly turned into a deeper issue involving the operating system, networking stack, and security software.
This post outlines what happened, how I diagnosed it, and why I ultimately chose to roll back to a stable version of macOS — a decision made painless thanks to a disciplined backup strategy.
The Symptoms
After upgrading to a macOS 26.5 beta build, the system began behaving inconsistently:
- Wi-Fi had no internet connectivity
- Ethernet worked, but only partially
- Some websites (such as banking) loaded correctly
- Business-critical apps like FileMaker could not connect to FMPHost
- Sophos Endpoint became inaccessible
This wasn’t a complete outage — it was worse: partial connectivity.
Initial Diagnostics
The first step was to determine whether the issue was external or local.
A quick port test confirmed that the FileMaker service was reachable:
nc -vz a731293.fmphost.com 5003
The connection succeeded, which ruled out:
- ISP issues
- Router/firewall problems
- External service outages
At this point, it was clear the issue was local to the Mac.
What Was Actually Broken
The problem was caused by a combination of:
- macOS beta networking instability
- A corrupted or incompatible network extension
- Interference from endpoint security software
Modern macOS versions rely heavily on network extensions for traffic filtering. When these break (especially after a beta update), they can leave the system in a half-working state:
- Some traffic flows normally
- Some traffic is silently blocked
- Applications behave inconsistently
Exactly what I was seeing.
Why I Didn’t Keep Troubleshooting
At this stage, I had two options:
- Continue debugging an unstable system
- Cut losses and rebuild cleanly
I chose the latter.
When the foundation is compromised, rebuilding is often faster than repairing.
The Recovery Strategy
1. Download a Full macOS Installer
Instead of relying on Software Update, I used Terminal to download a clean installer for macOS Sequoia:
softwareupdate –list-full-installers
softwareupdate –fetch-full-installer –full-installer-version 15.7.7
2. Create a Bootable USB Installer
sudo /Applications/Install\ macOS\ Sequoia.app/Contents/Resources/createinstallmedia –volume /Volumes/installer
This created a fully bootable installer.
3. Perform a Clean Installation
- Boot from USB
- Erase the internal drive
- Install macOS from scratch
4. Restore Using Migration Assistant
Direct migration from the beta system wasn’t possible, as macOS does not support migrating from newer to older versions.
Instead, I migrated from another Mac running the same stable OS.
5. Restore Critical Components
- User data migrated cleanly
- Windows 11 VM restored from backup
- Key apps reinstalled:
- FileMaker
- Sophos Endpoint
The Result
After the rebuild:
- Networking was fully restored
- FileMaker connected without issue
- No residual beta artefacts remained
- The system was stable and predictable again
Downtime was minimal thanks to preparation.
Key Lessons
Beta Software and Production Don’t Mix
If your system relies on business-critical tools, avoid beta OS builds.
Partial Connectivity Is a Red Flag
If some services work and others don’t, the issue is usually local. not the network.
Backups Are Only Valuable If They Work
Backing up the Windows VM separately made recovery fast and painless.
Rebuild Beats Repair (Sometimes)
When core system components are unstable, a clean rebuild is often the fastest path forward.
Control Your Install Process
Using full installers and bootable media gives you complete control and avoids surprises.
Final Thoughts
This experience reinforced a simple idea:
A system should be rebuildable at any time, not just repairable.
With the right preparation, what could have been a major disruption turned into a straightforward recovery.
If you’re running a mixed environment with macOS, virtual machines, and cloud services, the takeaway is simple:
Stability isn’t luck — it’s design.









