I’ve watched that clip and right from the start the shield for your senrty on the minimap is flashing. It stops briefly and then starts again (just before you arrive back at the sentry). It’s at this point (the break in flashing) that Oscar Mike stopped shooting and dropped his ult, which finished off your shields (you can see that the shields weren’t dropped completely by his ult, it had only just started before you arrived).
Do you have any footage prior to this? That would show whether or not the shield flashing occurred or not.