MacOs BigSur update 11.2.3 hangs with Error Domain=SUMacControllerError Code=7749 in logfile

Question

My iMac (Retina 5K, 27", 2020) is not updating to latest MacOS BigSur 11.2.3 from 11.1.

It hangs in the UI with "10 minutes left" in the progress bar. The install.log file exposes the following error messages (see below). Any idea what could cause this issue? Found nothing on google for the error message.

021-03-13 20:25:03+01 imac-ts SoftwareUpdateNotificationManager[764]: Successful call to queueAutoUpdatesForLaterWithCompletionHandler
2021-03-13 20:25:03+01 imac-ts SoftwareUpdateNotificationManager[764]: SUAppStoreUpdateController: install later for <none>
2021-03-13 20:25:03+01 imac-ts SoftwareUpdateNotificationManager[764]: SUAppStoreUpdateController: Triggering user side stash early for later updates
2021-03-13 20:25:03+01 imac-ts softwareupdated[273]: No keys specified for install-later registration
2021-03-13 20:25:03+01 imac-ts SoftwareUpdateNotificationManager[764]: SUOSUAuthenticationManager: No LocalAuth required
2021-03-13 20:25:03+01 imac-ts softwareupdated[273]: Queued (
      "<SUOSUProduct: MSU_UPDATE_20D91_patch_11.2.3>"
    ) for later
2021-03-13 20:25:03+01 imac-ts SoftwareUpdateNotificationManager[764]: SUOSUShimController: Armed: 1, with mode: 1, date: (null), updates queued for later: (
      "<SUOSUProduct: MSU_UPDATE_20D91_patch_11.2.3>"
    )
2021-03-13 20:25:03+01 imac-ts SoftwareUpdateNotificationManager[764]: Failed to create stash & update local policies: Error Domain=SUMacControllerError Code=7749 "[SUMacControllerErrorCommitStashInvalidState=7749] Committing the stash requires a valid prepare yet none is currently available (currently preparing)" UserInfo={NSDebugDescription=[SUMacControllerErrorCommitStashInvalidState=7749] Committing the stash requires a valid prepare yet none is currently available (currently preparing), NSLocalizedDescription=Sichern der Benutzeranmeldedaten f<C3><BC>r das Softwareupdate zurzeit nicht m<C3><B6>glich.}
2021-03-13 20:25:03+01 imac-ts SoftwareUpdateNotificationManager[764]: Successful call to queueAutoUpdatesForLaterWithCompletionHandler

Answer 1

The solution to this was constantly trying to reboot.

I have left the Mac between 1 and 3 hrs between different attempts.

Then stopped the round and rebooted, retry.

On third attempt the OS was finally installed.

I do not know what the problem was.