I am using sandbox apks from here:
- App Updater: com.clover.appupdater-1147.apk
- Clover: com.clover.engine-2023.apk

The only difference from the instructions is that after I added the Clover account and adb reboot, the app updater does nothing by itself. I'm not sure if you are missing a step from the instructions, I had to add the App Updater account manually and turn on sync for it. Then I immediately get the notification to download the apps.
I can see that syncing the account after this failure kicks off the download process again but I can't get passed the first app, it appears to be totally stuck
EDIT:
I think this is a red herring, I am trying to update the apps on an older AVD now via the app updater and they are consistently failing so it looks like there's just something wrong in general with the latest sandbox apks it's trying to download.