Hello @Joe Lin, welcome to the Sonos Community!
I am sorry to hear you are experiencing connection issues within your Sonos system.
Please have a look at our Support Article Reduce wireless interference which includes some basic troubleshooting steps and information that can assist you, with the main one being a network refresh to all networking devices involved.
Start by rebooting your Router → Sonos → Controller (smartphone/tablet).
As @AjTrek1 suggested, I would also recommend you reach out to our Support Team for live troubleshooting if you are still experiencing this after trying the above.
They have tools at their disposal to provide you with information specific to your Sonos system and what it reports.
I hope this helps.