I'm pretty sure there is "voter fraud" in every election that is at least state wide. Some of it could be "technical" violations or unintended, like taking someone's absentee ballot to drop it off when it's against the rules to do so (the person is not a relative, whatever). Some of it is intentional, ballot harvesting, but I think that is meant to impact some local election likely to be decided by a few votes. The logistics of setting up a major voter harvesting operation "under the radar" strikes me as nearly impossible.
But that doesn't mean some folks don't "raid" old folks homes to collect absentee ballots. But to do this to garner 10,000 of them or more seems impracticable.
I also doubt many "illegals" vote because their main objective is to stay off the radar. I've read some folks registered inadvertently when they are green card types or students when they get a DL because they didn't understand the rules.