The 18252 release notes confirm an older skip-ahead reported bug is now in Fast-ring: Settings app is crashing when invoking actions on certain pages. This includes “Check online for updates from Microsoft Update”.
Since this option does not have any schedule and can be triggered only manually, your Insiders for Business cannot update to the next insider release 18262.1000, if the machine is domain joined and configured to automatically get updated via ConfigManager or WSUS, the “Check for updates” button goes to the internal resources only.
As a workaround, delete the WSUS keys in the registry:
Restart the Windows Update service if running and “Check for updates” is able to get the insider release.
The 18262 release notes have this under ‘fixes for PC’, but I can still reproduce the bug.