I have just found the solution to my error 0x80073D12 "Something unexpected happened"
I have previously successfully installed and uninstall Halo CE and Halo 2.
Recently I tried to download Halo 3. The problem occurred after I had downloaded almost 7 GB and I couldn't resume the download.
Also the app of MCC wasn't in the list of apps so I couldn't uninstall it.
I had my installation in a different SSD (G) than the windows installation (C). I have found that the files became visible only while the MS store was trying to resume the download in G/Program Files/ ModifiableWIndowsApps/HaloMCC/
I deleted everything one by one and I resumed downloading. Of course now I have to download again all the 78 GB of MCC and Halo 3 afterwards.
I have previously successfully installed and uninstall Halo CE and Halo 2.
Recently I tried to download Halo 3. The problem occurred after I had downloaded almost 7 GB and I couldn't resume the download.
Also the app of MCC wasn't in the list of apps so I couldn't uninstall it.
I had my installation in a different SSD (G) than the windows installation (C). I have found that the files became visible only while the MS store was trying to resume the download in G/Program Files/ ModifiableWIndowsApps/HaloMCC/
I deleted everything one by one and I resumed downloading. Of course now I have to download again all the 78 GB of MCC and Halo 3 afterwards.