If a monitored device is up for more than 1.3 years, the UpTime displayed may be incorrect.

If a network device (switch, router, server) has been online for more than 1.3 years, the SNMP counter sysUpTime may roll over. The SNMP sysUpTime counter is a 32bit counter that tracks hundredths of seconds that the system has been online. This
counter will wrap around after 1 year, 18 weeks, 6 days, 2 hours, 27 minutes, 52.95 seconds.

When the SNMP standards committee created the specification for the sysUpTime counter, it was expected that network equipment would be rebooted sometime within a year timespan (either for OS upgrades or general equipment preventive maintenance cycles).