Ok, so this might be my OCD acting up, and not a real problem, but here goes:
I've noticed that if I'm coasting (or really soft-pedaling) and then start pedaling again the crank rotates forward a little bit before my cassette/freewheel engages -- maybe 1/16th of a crank rotation, but probably less. The rotational distance the crank takes to engage the back wheel seems to be taking longer than I remember, which is why I noticed it. I'm assuming that there's something weird going on with the freewheel/hub assembly, but I don't know if I'm imagining things.
Remember that the crank angle needed to engage the freewheel pawls depends on the gear. (The angle at the wheel is constant and depends on the make of freewheel.) In a high gear, engagement will happen with very little crank motion, and in a low gear, more crank motion is required.
Maybe your riding style has changed toward spinning faster cadences in lower gears...?
I've had several since 1999 but have settled on my beloved 2001 Litespeed Tuscany and my latest, a 2015 Cannondale SuperSix EVO carbon
You could remove the freewheel and apply some light lube (Triflow) to the back of the freewheel. If needed, whack the freewheel with a small hammer to free the pawls.
That did the trick on a bike I worked on yesterday.
My bikes: 2001 Litespeed Tuscany---2015 Cannondale SuperSix EVO carbon