Hello, friend!
The MA5821 belongs to the Multi-Dwelling Unit(MDU) on the Access network, it is not a switch device.
According to your problem description, I cannot accurately locate the fault.
If the Internet access service is abnormal, check whether the downstream service of the OLT and the upstream port of the MA5821 is normal.
To configure and troubleshoot related services based on the MA5821 product documentation, click: SmartAX MA5821
Thanks!