I know it is kinda late but I thought if someone else has the same issue it might be useful to have another possible solution.
I had the same issues: first i had to enable i2c manually and then i got this AsyncWorker error.
In my case the issue was that explorerhat was always on version0.4.2 even with updating/upgrading. I fixed it by removing it entirely: sudo apt-get --purge remove python3-explorerhat
and then following the steps indicated by sandyjmacdonald: Explorer HAT install instructions - #4 by sandyjmacdonald
git clone http://github.com/pimoroni/explorer-hat
then
cd explorer-hat/library
then
sudo python setup.py install
now it is on version 0.5.1 and works just fine.