Press bottom right Alert text area:
Alerts tab is empty:
Changing distance to 5 km or 20 km and back to 10 km and alerts are shows correctly.
Yes, this is a known comm bug, already known by niantic.
@HopeaKotka we're still working to fix COMM. In the meantime, if your COMM feed is empty, you can force it to reload by tapping a different distance range (for example, 5km or 20km) to load COMM updates.
This has been an issue for me as well, but the behavior applies to all distances, not just 10km.