Same here, a LOT of "EXIT_TIME_LIMITE_EXCEEDED" erros.
It's a problem of VirtualBox??

From what I learned over at Kryptos@Home, which used Boinc2Docker as it's initial WU, Boinc2Docker does not work well (or at all) with Virtual Box 6.x.
My guess is to run NanoHub you need to rollback to Virtual Box 5.2.44 (last update in version 5).
Check VBox manager (after restarting computer or restarting the VBox service) and see if you have hundreds of invalid VM's built up.

My 5.1.28 VBox machine is running these WU's (badly, with many invalids) and my 6.1.2 VBox machine has not completed any successful WU's even though it appears to be running them properly (after I limited the WU's to 4 max_concurrent in app_config.xml).
I have some maintenance to perform on that machine and let you know if it succeeds to run a valid WU today.

My guess is to run NanoHub you need to rollback to Virtual Box 5.2.44 (last update in version 5).
Check VBox manager (after restarting computer or restarting the VBox service) and see if you have hundreds of invalid VM's built up.

I've done the rollback to 5.2.44 (and i install the extension pack).
I'll see if it's better.

My 5.1.28 VBox machine is running these WU's (badly, with many invalids)

That was a separate issue.
Once I took Jim1348's advise about installing a RAM cache, the machine w/ VBox 5.1.26 is cranking through NanoHub WU's with no invalids.