How big is your image to start?
Could you give a screenshot to show what happens in this clip goes red when scaled up to much?
You've likely found the limit of your GPU memory for your frame size. There's very specific math involved how much memory it takes to process frames at specific resolutions, but I can't remember how that works. If you're getting a red bar then it's probably falling back to CPU processing. What kind of GPU do you have, and how much VRAM does it have? As a test to confirm this, have you switch to CPU-processing to se if it also takes as long? You don't have to do the full test, probably just a fraction of time so it doesn't take 30 minutes.
The pic is very small 230*450.
GTX 1060 6 GB.
What kind of screenshot? Drag the pic to the timeline, drag transform effect on it. Change the scale in the transform effect to 307% - everything is fine. Hit 308% - it is red.
It is definitely a PP bug.