Thanks for Shoya Shiraki. But the member is a normal Android user. I found the member's account is foreign account. It seems to be the main cause.
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It seems to be related to "User consent"
userId ID of the source user. Only included in message events. Only users of LINE for iOS and LINE for Android are included in userId.
https://developers.line.biz/en/reference/messaging-api/#source-group https://developers.line.biz/en/docs/messaging-api/user-consent/
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