property "mode" change from "active" to "standby" cause replyToken missing

Pre condition, Condition to reproduce

Try to trigger bot to reponse flex message when user interact with rich menu on LINE OA Tops Thailand

Issue/ Error Message details

no flex message reponse

Accompanying respective source code

Resolution Tried

try to check log, found that property "mode" change from "active" to "standby" according to document https://developers.line.biz/en/reference/messaging-api/#common-properties

Reference information (Version / Platform/ environment)