When I have the chain in the middle ring AND the either of the 2 lowest (biggest) gears in back, sometimes with enough force the chain pulls off of the middle ring. If I'm lucky it'll catch on the inside granny gear and I can recover, but more often it's off altogether.
This mostly happens during a climb when I stand up. In my opinion my chain line seems reasonable, and I never use those 2 big gears in back aside from climbing. On flat ground it shifts smoothly, no rubbing. It doesn't matter if I spin or mash, UNLESS I'm in that bizarre combo of middle ring and the 2 biggest rear gears.
This is an 8 speed bike. The middle ring has 38t, the biggest in the rear is a 32. It came stock with a shimano 32t cassette, but when that wore out I got an SRAM chain and cassette.