问为什么Firebase消息传递web客户端messaging.getToken()有时会产生不同的令牌？(相同的浏览器，相同的标签)

EN

// Get registration token. Initially this makes a network call, once retrieved
// subsequent calls to getToken will return from cache.
messaging.getToken({ vapidKey: '<YOUR_PUBLIC_VAPID_KEY_HERE>' }).then((currentToken) => {
  if (currentToken) {
    // Send the token to your server and update the UI if necessary
    // Occasionally, I received a different token here.
  } else {
    // Show permission request UI
    console.log('No registration token available. Request permission to generate one.');
    // ...
  }
}).catch((err) => {
  console.log('An error occurred while retrieving token. ', err);
  // ...
});

FirebaseError: Messaging: A problem occurred while unsubscribing the user from FCM: FirebaseError: Messaging: A problem occurred while unsubscribing the user from FCM: Requested entity was not found. (messaging/token-unsubscribe-failed). (messaging/token-unsubscribe-failed).
    at _callee8$ (eval at <anonymous> (app.js:2982), <anonymous>:572:45)
    at tryCatch (eval at <anonymous> (app.js:6025), <anonymous>:62:40)
    at Generator.invoke [as _invoke] (eval at <anonymous> (app.js:6025), <anonymous>:296:22)
    at Generator.prototype.<computed> [as next] (eval at <anonymous> (app.js:6025), <anonymous>:114:21)
    at step (eval at <anonymous> (app.js:636), <anonymous>:17:30)
    at eval (eval at <anonymous> (app.js:636), <anonymous>:28:13)

curl 'https://fcmregistrations.googleapis.com/v1/projects/chatisfy-d2721/registrations/cD0VOZLBLdaVymfaUbQyE4:APA91bHj2qCU02_Sib6gEPw3VuPTDkjpj0ZVpgmWYaaHESpTjpH-uwY5JX5mn_W7YhJ1AOMp4dNnwpUffs7SQkBs1UYGGie0o4u_i-OjYY5Q5uRSl3pZQoRGVzwNXxe0lDrQIHD4SN5A' \
  -X 'DELETE' \
  -H 'authority: fcmregistrations.googleapis.com' \
  -H 'sec-ch-ua: " Not A;Brand";v="99", "Chromium";v="96", "Google Chrome";v="96"' \
  -H 'sec-ch-ua-mobile: ?0' \
  -H 'user-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.110 Safari/537.36' \
  -H 'content-type: application/json' \
  -H 'accept: application/json' \
  -H 'x-goog-api-key: AIzaSyDFP12b-P9JwiDvJuqsWVz6k2Z8ww6_2-E' \
  -H 'x-goog-firebase-installations-auth: FIS eyJhbGciOiJFUzI1NiIsInR5cCI6IkpXVCJ9.eyJhcHBJZCI6IjE6NTI4MTcxMTk2MzYxOndlYjowMWQyMzQ4ODNiYWQ3NWU5MmYxMjE4IiwiZXhwIjoxNjQwMjUwMDc2LCJmaWQiOiJjRDBWT1pMQkxkYVZ5bWZhVWJReUU0IiwicHJvamVjdE51bWJlciI6NTI4MTcxMTk2MzYxfQ.AB2LPV8wRQIhAL4F96JV_fSn2LHzpBiYDWnOVcpA7zBT35lvWz0WqS8fAiAlC28Un0hO2uD6_DuRPnHdqnO_5wIr-byID127niFXRg' \
  -H 'sec-ch-ua-platform: "macOS"' \
  -H 'origin: http://localhost:8080' \
  -H 'x-client-data: CJO2yQEIpbbJAQjBtskBCKmdygEInvnLAQjmhMwBCLWFzAEIy4nMAQjSj8wBGI6eywE=' \
  -H 'sec-fetch-site: cross-site' \
  -H 'sec-fetch-mode: cors' \
  -H 'sec-fetch-dest: empty' \
  -H 'referer: http://localhost:8080/' \
  -H 'accept-language: en-US,en;q=0.9,zh-TW;q=0.8,zh;q=0.7,zh-CN;q=0.6' \
  --compressed

{
  "error": {
    "code": 404,
    "message": "Requested entity was not found.",
    "status": "NOT_FOUND"
  }
}