It looks like there were some changes to the implementation between those versions, mainly this this bug fix.
If you downgrade to 6.1.2, what does the usage drop to?
My experience with the current stock blur/shadows in JUCE is that they are best avoided. They are expensive, inconsistent with other tooling and many of us use our own implementations.
For alternatives (in case you don’t end up with a fix), I recommend checking out FigBug’s stack blur. There’s also a PR open for a modern StackBlur implementation.
@t0m gave a presentation last night saying improvements to the animation system and rendering in JUCE might be around the corner (exciting!). Perhaps some of these effects will be modernized along with that too?