Agent Timeline is showing blank for many active users in live or historical data. Realtime can be very data intensive, so if you are running low on memory(RAM) it can cause this symptom.
White wallboards can indicate a few issues, but the primary one is a lack of resources on the local machine viewing the Real-time Agent Timeline.
Close any other tabs on Chronicall, so Agent Timeline is your only Chronicall tab.
Close out of any other open applications that may be using up your computer's resources, such as internet browsers and other applications.
Test loading the dashboard again to see if it helps, it will now have additional available memory (RAM) to display the Agent Realtime wallboard.
If the issue persists, the issue may lie in an outdated 32 bit Chronicall Desktop installation.
Uninstall Chronicall Desktop locally in the apps & features for Windows,
Reinstall Chronicall Desktop using the below article.
3.12 and older
4.0 and newer