Multiple IPsec dynamic peer tunnels

Hi guys, I have a setup where I have 10 peers connecting to my main office Mikrotik. The main Mikrotik has the 0.0.0.0/0 and generate policy configuration. All clients have dynamic IP’s. They all connect fine but some are randomly dropping after an hour or so. I see in the main Mikrotik under IPsec/Installed SA’s I can see multiple (4 or 6) SA"s from the same client. One pair will be “live” with the others passing no bytes..Why is this? I have DPD Interval set to 60 sec on the main Mikrotik is this correct? should this detect he dead peers and flush them? Am I missing something?
Cheers