Effects Lag when adjusting values - SOLUTION!

Hoping this helps someone out there...

We're using the latest version of AE 2018 on Windows 10 pro 64. We work with 5k RED footage, 4800x2700.  We find when using effects such as levels on an adjustment layer, the system will lag terribly once you add more than one instance of the effect (meaning the composition window updates very slowly while adjusting values).  So for instance, if we create an adjustment layer above our footage & add one instance of levels, it works great.  Add one more and we can barely do anything without significant lag.  It will become worse and worse the more copies of levels (and certain other effects) are added.  This is also the case with 1080 footage, but you have to add 4+ effects before it becomes noticeable.

Here's a thread that describes the problem but became so bogged down with posts that I decided to make a new discussion:

After Effects 2017 - Effects Lag when adjusting values

The bug is somehow related to the size of the adjustment layer itself.  A small adjustment layer will work with little to no problem.  Our large 4800x2700 adjustment layers won't work at all.

The fix is simple (though it makes no sense):  create an adjustment layer at 640x360 and scale it up as necessary (753% in our case.)  IMPORTANT - scaling will feather the edges so make sure you overscale the layer beyond your comp borders.

That's it.  Works perfectly.  A fix would be great for this, though - I'm sure it's caused many a headache.