eero Pro (2nd generation) will not connect one device

The checks in more detail

The eero Pro supports Wi-Fi 5 on 2.4 and 5 GHz and uses one name for both, and a very old or small device, such as a smart plug, can only use 2.4 GHz and may fail to find it on a shared name. Bring it close to a unit while joining. Turn off the private address on phones for this network, since random addresses cause some routers to refuse them. Open the eero app and look at the device list: does the device appear, is it paused or blocked by a profile, and does it have an address assigned? If the router's address pool is full, a rare case, remove old devices.

Newer devices with Wi-Fi 6E or Wi-Fi 7 only use their lower bands with the eero Pro, and a few devices that require WPA3 may need the eero's security setting changed, though WPA2 is the default. Update the eero software in the app, since updates may arrive for older units for security, and update the device. If the eero Pro is several years old, a unit that has become unstable can cause refusals: check each unit's status in the app and its uptime, and replace or reseat a unit that keeps going offline. If the device connects but has no internet, test other devices to separate a device problem from a network one.

If a device fails on every network it is faulty. If the problem remains, eero support can read the logs, though the original Pro may be near the end of its support. If your smart devices keep dropping from the network after a power cut, the order of restart matters: modem, then the gateway eero, then the other units, then the devices. A device that comes up before the network is ready may fail to connect and need a reboot of its own, so give the network a few minutes before starting them. A reserved address in the app for a device that must stay at a fixed place helps too.