With the Color Range keyer selecting colour has stopped working for some footage
In AE CC 2017, I have a composition (A) where the footage is from another composition (B) and this composition (A) had 11 colour range keys on it. And they had worked at one point and I had selected the colour to key. Now, when I add a color range key to the composition, pressing the icon to select the colour to key switches to the (eyedropper?) icon but when I place it over the footage to select the colour it changes back to the normal mouse pointer so doesn't select the colour.
The video that's started having a problem is quicktime pro-res - even though colour range key worked okay on it previously (note: I'm using Windows 10).
I've also tried using the footage from composition (B) in a new composition but that does the same thing (just shows mouse cursor over the footage). But if I put a color range effect on a video rendered with quicktime jpeg2000 it works as normal (shows the eye dropper when cursor is placed over the footage).
I've tried loading the pro-res video into a brand new (empty) project and the color range keyer works as normal there (shows the correct icon when placed over the footage).
Is there a quick/simple way of fixing it in AE CC 2017 (there's an issue with the project when you load it into AE CC 2018 too, and that doesn't load a quicktime jpeg2000 compressed file and I doubt it will render to it either) so in the main project the color picker works properly with the pro-res video like it had done when I added the previous color range effects?
Note: I've tried turning hardware acceleration off in "general->display" but that didn't make it work again with the pro-res based comps in the main project.
