Skimmer keeps spontaneously overflowing.

[gobytron]

I always found that one of the most overlooked skimmer adjustments is how deep in the water in your sump it sits.

Try building a stand for your skimmer out of egg crate (or anything, I always used egg crate because it's handy and easy to clean/adjust) and raising it inside your sump.

Then set your skimmer to skim to your preference with the new depth.

This might not solve whatever is changing in your water column to create more skimmate all of a sudden, but it will stop your skimmer from overflowing when that does happen.