Garden Guy wrote:

[....]
people *might* put on it (those chemicals have long since degraded and
broken down before the grass is cut and will further degrade when
composted).

wrong....

when creating pasture grass for animals to graze on
you'll learn after doing some research and reading how
there are a vast number of lawn products that are strictly
forbidden and extremely unwise to use on pasture grasses.
these are products commonly used by the typical home owner
seeking a green lush healthy lawn. the reason behind this
is because these products do indeed end up in the grass and
are then ingested by the animal doing the grazing.

as for your problems with mulching, I suspect you're waiting
to long in-between cuts and therefore producing more clippings
than the lawn can properly absorb before your next cut. for
example: the typical recommendation for mowing fescue is to
mow when the grass reaches 4 inches in height and to cut back
to three inches. when mulching the 4 inch height the cut
should only remove 1/2 inch leaving the height at 3.5 inches.
proper mulching techniques require more frequent mowing. so,
cut and mulch at a height of 3.5 to remove 1/2 inch returning
the fescue to the recommend height of 3 inches.