An issue existed where partially entered passcodes may not clear when the device went to sleep. This issue was addressed by clearing the passcode when a locked device sleeps. This issue is fixed in watchOS 5.2. A partially entered passcode may not clear when the device goes to sleep.
Source: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-8548
Reference (s):
- https://support.apple.com/HT209602