I have noted that this happens whenever I add a largish image to an Atlas - typically these are images I use for backgrounds. I always reduce my image sizes using tinypng but even so full screen backdrops weigh in at several 10s of Kb.
Each time I do this the IDE becomes momentarily unresponsive. Then it vanishes from the foreground. A few seconds later when I foreground it again its size has changed.
All of this on a Windows 10 machine with 32Gb of memory.
A related question - I have often wondered if it even serves any purpose tinypng’g my images. I am guessing that Defold builds a single image when I add a new image to an Atlas a bit like a tilemap and does all the hard work required to keep the composite image as compact as possible?