Any ideas?
The map is usually missing when GPS is not enabled, or when you do not get the lock on the GPS satellites, which can happen in bad conditions (high-rise buildings, dense vegetation, watch under the water surface,...) , or when the ephemeris file data (EPO or CPE) is expired (What Is EPO or CPE on a Garmin Product? | Garmin Customer Support).
If the watch was recently updated, make sure to reboot it first.