Tasks do not get processed anymore after an upgrade from 4.1.9 to 4.2.1 or later.  You see Awaiting assignment as the task state.

Before you start fixing this, make sure that no intelliVM profiles are beeing customized.
This would take all intelliVMs offline resulting in the same message for the tasks.
Go to Analysis Settings / IntelliVM Profiles in the UI.
Make sure that all profiles show Ready for the Status.
If this is true continue below.

To fix this, please log into the MAA via SSH using the g2 user. 

Then run these commands 

python /opt/mag2/github/Malware-Analyzer-G2/utilities/mag2.py -r localhost import-ivm-plugin --owner _SYSTEM_ --magic system:util:ivm --extension "" /opt/mag2/usr/share/mag2/ivm/ivm-service-x86.exe
 
python /opt/mag2/github/Malware-Analyzer-G2/utilities/mag2.py -r localhost import-ivm-plugin --owner _SYSTEM_ --magic system:util:ivm --extension "" /opt/mag2/usr/share/mag2/ivm/ivm-service-x64.exe 

python /opt/mag2/github/Malware-Analyzer-G2/utilities/mag2.py -r localhost import-ivm-plugin --owner _SYSTEM_ --magic system:svcplugin:ivm --extension "" /opt/mag2/usr/share/mag2/ivm/emet.lua 

After this, the tasks that are still waiting for assignment may or may not finish. If they do not start processing after a few minutes, you need to clear out the task queue and recreate the task.

To do that run this command from the CLI: 

curl -X POST http://localhost/rapi/system/purge_task_queues 

Recreate the tasks and they should now complete.