It happened once to opposition team approx 1-2 months ago, where I was attacking and with 2 mins to go, everyone of the other teams war members became available to attack.
Happened against us just there, where 3.5 hours to go, we were ahead by 400 or so, with no possibility of enough of our members returning for their team to win. 2.5 hours to go, approx 8 of our members returned. Looks like it will lead to us losing the war. This is very frustrating