DOA has a notoriously terrible netcode. But try to check your internet. Is your internet enough? Router and modem are stable? Also try to use LAN cable to see if the problem persist.
Because DOA is peer-2-peer. If we are playing together online, that means it's like we are holding into a rope on each end. If your hand (in this case, the internet) isn't stable or strong enough to hold, we'll be separated no matter how strong my hand is.