When I use File->Render Animation to export out individual frames for animation, if files already exist in the target folder location with the same names, the application stops responding and all ui elements become greyed out and unresponsive.
That sounds like the application is freezing? Is there any way you could give us more detailed information on what is going on? Could you run Krita in a terminal for instance? And what kind of file is it that you are exporting? How much ram do you have?
Created attachment 105701 [details] animation export settings
I actually tried to recreate the error again and was unsuccessful. Now the images are created in the folder with an additional "~" added to the end of the old filenames since the filenames were already present. When I had the issue, I was exporting .png files with the settings shown in the attached image. My machine has 16GB of ram available.
With 4.0 beta 1, Krita asks to overwrite the existing animation frames, so this is fixed by now.