Hi @Nero Liang, welcome to the Box Community!
These notifications often appear when a third-party program automatically traverses a user's Box file tree on their local device. For more information, please check out: Troubleshooting “Unable to Open Folder” Notifications.
To resolve, please advise her to work with their IT or Help Desk to exclude the following Box directories from local security scans:
Windows |
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C:\Users\username\AppData\Local\Box C:\Users\username\Box C:\Program Files\Box |
Once the Box directories have been excluded from local security scans, she should no longer experience increased CPU usage, network traffic, degraded performance, or “unable to open folder” notifications.
If she continues to experience the issue, please submit Box Drive Logs and open a support ticket for further assistance. 
Dear Jey,
However, the folders that my colleague received notifications about are ones she cannot access and belong to other departments. Could you explain why this is happening? Is it related to the Box service error from last week?
Hello @Nero Liang, thanks for your response.
The known issue from last week impacted Box Drive uploads/downloads. However, there is no issue related to the error your colleague has encountered. To determine the root cause, it's important to check the shared content and the Box file tree on their local device, as outlined here: Troubleshooting “Unable to Open Folder” Notifications.
For further investigation, I highly recommend submitting the Box Drive Logs from your colleague and submitting a support ticket so our Product Support team can assist.
Looking forward to sorting this out. 