I have a habit of performing updates via Synaptic. Sometimes I do this immediately upon starting a session. Often this activity is obstructed and a message appears advising me that only one software management tool is allowed to run at the same time. I have learned that this is invariably due to an active unattended-upgrade process. I am no longer mystified about it.
However, it would still be nice if some kind of tell-tell were to appear somewhere on the screen to advise us when this process is underway. Then, when the upgrade is finished and the tell-tell disappears, we could carry on with the operation that had to be postponed, be it apt-get, dpkg, gdebi, Synaptic, or Installing Updates.