Hello,
1. Whether do you login ONU via web and click "submit" any interface ?
If you click "submit" any interface on web of ONU, you will save configuration into flash of ONU that the configuration is date of router wan connection before you configure router date.
So you configure bridge date for ONU on OLT, Because there are still router wan connection on ONU, so router wan connection is still valid.
If there are router wan connection on ONU, priority of router wan connection is higher priority of bridge mode when vlan of router wan connection and bridge mode are same.
2. Solve the issue that you need run " restore factory" for ONU on OLT after you change router to bridge mode.
ZXAN(pon-onu-mng)# restore factory