Liquify tool stops working throughout CC2019 project

I have 2 employees having this same issue on separate projects/machines; when Liquify is used on multiple layers in CC2019, at some point it just stops working in the entire project, i.e. when a brush tool is selected, the mouse stays as the default pointer instead of turning into a brush (though other settings like Percentage can still be changed on the existing effect). Subsequent Liquify effects on new layers, within new compositions, etc, completely stop letting brushes be selected also, meaning that Liquify just stops working across the entire project. I've never seen this in CC2018 or earlier. Does anyone know a fix for this? Playing around with memory, GPU, etc, doesn't seem to help. I'm wary of CC2020 as we were running into corrupted projects that were destroying all of our work. Thank you!!