When I flew ORD-LHR-FCO back in January my ORD-LHR AA flight departed over three hours late owing to a missing pilot. So the original 5-hour layover at LHR was whittled down to about 1.5 hours. Upon landing at T3 I quickly made my way to T5, and when I scanned my AA-issued BP at the T5 fast lane checkpoint I got the dreaded red warning. So I went to the BA staff at the fast lane counter, and she couldn't get the BP to work wither and couldn't understand why. She tapped on the keyboard for a bit and eventually re-issued the BP, which worked this time. So I'm now wondering if it's possible that I might have been offloaded from the FCO flight due to AA86's late arrival from ORD. I was in J and the BA flight to FCO was rammed full in economy but at take-off there were a couple of empty seats in the Club cabin, which might explain why the BA lady at the fast lane counter was able to reissue the BP, if I had indeed been offloaded.

So I guess that going forward the risk of being offloaded by an overzelous computer is another factor to take into account when planning a trip involving an LHR layover..