That's the first I've heard of this issue. The question is whether this is caused by the code in the file or the way you moved around in it. Can you try closing and reopening the file. Then scroll using page down, pausing until the colors are rendered for that screen, then hit page down again. Does that reproduce the blotchy areas without the coloring? If so, it could be that those areas contain elements too complex to be analysed in the time allotted. You can increase the value of "Timeout after (ms)" in Tools > Options > Editing > Context Tagging, in the "Symbol coloring performance" section at the bottom of the screen. Maybe increase this to 2000 and see if the blotchy areas go away.
If you could send us the file and a screen shot of the uncolored areas, we can try some tests to see what's going on.