I have the same problem, when someone logs out, others can't access doors or chests for a minute or so... don't know any workaround sorry.

Also sometimes no one is able to connect and I fix this by restarting the server (I use dathost)

also when Mistlands came out yesterday we started getting lags and disconnects every few minutes on our dedicated server, it's impossible to enjoy the new content with this... Wonder if it's a hosting issue or Valheim issue