I found that if I didn't turn on arc for a few days, arc couldn't connect to the core

Hi @junbiao_jiang,

There are several more involved workarounds discussed in threads such as this one: Is there anyway to log remotely to restart the Roon Core? - #18 by Johnny_Ooooops

I recommend searching around the forum, but keep in mind that network-external access to your Core (other than via ARC) is outside the officially supported functions of Roon, so we can’t give recommendations or advice beyond what other users suggest in #tinkering and #roon.