If you have more machines in your network than you have licenses, Avast! randomly decides which ones to license and which ones are not. It's stupid really. I have an Active Directory domain that has MacBook's joined to it, so when I do a discover task for AD computers, it brings them in. I have to manually delete them so that I can use all licenses on machines that actually need Avast.
You can request more licenses, or you can delete the machines from the EAC so they do not consume a license randomly, or you can rework your network/AD system so that machines that should not be licensed are not picked up by the discovery tasks.
It's not very practical to randomly assign licenses to machines that are discovered. It makes more sense to assign a license when the client is deployed.