It is a bug and we will fix it in 5.21.1.
Refreshes are too aggressive in Mendix 5.20.0 and that is still the case in 5.21.0. The data view should only update conditional visibility/editability when the object is refreshed, but now it accidentally calls
applyContext on all its children.
I'll get back to you with an ETA on 5.21.1.
We have run into a few issues with this in 5.20 as well. As far as I know now this behaviour has indeed changed in 5.20 (but was not documented in the release notes). This is not considered a bug by Mendix, the new behaviour is as it will stay.
For instance the microflow timer widget has been updated by Mendix to work correctly with this new behaviour, I am sure the same need to be done for other widgets as well.