The disocvery bot process page is not displaying for some users. Restarted the bot agent service still does not display. The users could access the page before today. Any advice?

If this is a cloud deployment then it may be a temporary issue. If on-prem deployment then you may want to check the firewall/network settings for the affected users if any new Group Policy might be interfering with the communication.

It would also be a good idea to re-assign the relevant roles to the affected users, regardless of the deployment type.