Hello @KCmikee
I assume the first one in that chain is the one set up as a router+firewall and the second two were added as secondary / point units? Beyond that, depending on how long those cables are, Cat 5 cables may not be able to successfully negotiate and hold a 1Gbps Ethernet connection, while Cat 5e would be able to. I would first check the Google Home app to ensure both of those secondary units are showing a connection type of "wired". If so, and the mesh test is still showing a "weak" rating for them, then I would focus on the cabling itself. If the first cable (between the primary and first secondary) can't hold a 1Gbps link speed, then it doesn't matter what speed the second cable (between the first and second secondary units) negotiates.
In addition, I would try to use an inexpensive unmanaged Ethernet switch instead of connecting them serially like this. You'll still connect the first unit directly to the fiber jack, but then you'd connect an Ethernet switch to the LAN port on that first unit. From there, connect each of the two secondaries independently rather than chaining them. If that cable is quite long, you might even benefit from putting Ethernet switches on each end. You might even consider one that has LED lights that indicate what link speed is being used.
