The problem could be in DHCP lease time unless the ethernet cable was unplugged. DHCP server assigns an IP to Reduxi Controller (or any other network device connected to this DHCP server) for a specific time, for example, 24 or 48 hours.
After 24 or 48 hours, the IP assigned to Reduxi Controller is changed, and you can not access Reduxi Controller over Reduxi Configurator using the old IP.
The solution is to scan again for Reduxi to get the new assigned IP from the DHCP server or to change the new configuration from DHCP to static mode.
Login to Reduxi Configurator, go to Settings -> System -> Network and change from DHCP type to STATIC.