Hi there @Clara!
First, remove your 2019.4 env (if you installed it before the fix was released):
conda env remove -n qiime2-2019.4 # or whatever you named your env
Then follow the official installation guide to get set up with the latest 2019.4. Once installed, run qiime info and check that q2-types is at 2019.4.1. That is all!
Please keep us posted with any more questions - thanks! 