This can happen due to 2 reasons
1. If agent has not allowed notification for Support.com Cloud in their respective browsers. Here are the steps to check this-
- Click on "Secure" or green lock icon before URL
- Check if "Notifications" are set to "Allow"
2. If some plugin is installed in browser to block notifications. To get to them, you have to click on the menu icon, then select Settings, scroll to the bottom and click on Show advanced settings, then click on Content settings under Privacy, and then click on Disable individual plugins