Before launching these nodes, I make sure that in the conf files I have the addnodes= lines pointing to my own nodes as well as those that are still online that might belong to the devs.
If that coin's client is identical to Bitcoin Core, you're using the wrong parameter.
It should be
addnode= without 's' and can be written in multiple lines if you need to manually add more peers.
If you have added other parameters, please tell us.
Sorry, I mistyped. I did actually use addnode= , in fact as I said at the time the blockchain gets stuck I do see the peers still connected, they just stop syncing.