I've fallen numerous times. SPD's on a MTB.
First got the bike in 2003 - feel fell a few times and switched to platforms with toestraps. I am more comfortable with toestraps than clipless.
Last year tried to give clipless a go again. A few falls on the street, mostly when I've had to make sudden, unexpected stops. Mostly on the streets I have time to plan my releases.
On the dirt I've fallen more often. Usually it's when I've had to make those sudden, unexpected stops again. And on uphills. I have the hardest time clipping out while going uphill. So much so that I typically put one foot on the platform side if I think I may not make it up the hill.
Also, on expected difficult rides for me, I'll switch to platforms/toestraps to stop the bleeding.
I think for me there may be multiple things at play.
Pedals with not so much use; bad knees and ankles that turn heel inward much easier than heel outward; and possibly cleat adjustment.