Download failed for Big Sur Beta 4 on Developer Transition Kit

I have been able to install betas 4-6. I had to use the Install Profile button on this page: https://developer.apple.com/download/ to get beta 4 installed but after that I have been able to use the standard update process off the About This Mac menu choice. The update to beta 6 was kind of clunky and it took awhile for the Restart button on the restart required notification to activate but it eventually worked.

I have the same problem. System says there's an update available, I'm trying to install it, it starts, but ends with an error. When running softwareupdate -ai under the console, I need to start it from a normal user (can't start it from root because if I do that, it starts asking for a password of some user that doesn't exist), it ends rather quickly with an error:

Code Block 
Failed to download & prepare update: Error Domain=SUMacControllerError Code=7721 "[SUMacControllerErrorPreflightWakeupFailed=7721] Failed to perform PreflightWakeup operation: [MobileSoftwareUpdateErrorDomain(MSU):MSU_ERR_INTERNAL_ERROR(7)]" UserInfo={NSUnderlyingError=0x14ee05710 {Error Domain=MobileSoftwareUpdateErrorDomain Code=7 "No service connection" UserInfo={NSLocalizedDescription=No service connection}}, SUMacControllerErrorIndicationsMask=0, NSDebugDescription=[SUMacControllerErrorPreflightWakeupFailed=7721] Failed to perform PreflightWakeup operation: [MobileSoftwareUpdateErrorDomain(MSU):MSU_ERR_INTERNAL_ERROR(7)], NSLocalizedDescription=Failed to launch the software update installer. Please try again.}

Tried both on Wi-Fi and wired connection, there's no problem with the Internet connection (I'm writing this post from the same machine).

I am still unable to upgrade beyond the original Beta software that came with the DTK - which has lots of odd behavior. Any update on how to update these?

I am still unable to install Beta 4. I get the classic "Download Failed" message after starting the update.

However, by visiting https://developer.apple.com/download/release/ in Safari on the DTK, I have been able to click "Download" next to macOS Big Sur, then Click Install via the App Store that pops up, and then Click Agree.

I now have BigSur installed successfully on the DTK :-)