This is a weird one. I live in a very remote area with no wired internet options, so I have set up a 4G router about 75 meters from the house in a spot where 4G reception is good enough. I'm running a 75m CAT7 ethernet cable with power-over-ethernet adapters on both ends to power the router and get signal back. The 4G router takes 12V input, so I worked out that using a 24V source for POE works out to the right amount when accounting for loss over the cable (this might be a completely nonsensical calculation as I generally don't know what I'm doing).
Now to the weird part. I have been using a mesh system to have WiFi in the whole house, with 5 different Huawei A1 units. It has been working fine for the past 9 months, and suddenly the units stopped being able to detect the ethernet cable when plugged into their WAN port. I've also tried an extra TP-Link Archer 4000 router, to no avail. What's worse, both my desktop computer and laptop gain a perfectly working access to the internet when I plug the exact same ethernet cable in them.
Needless to say I am baffled. It clearly isn't a problem with the 4G router out in the field: walking out the house and connecting to its WiFi network works fine. Moreover, it's not its LAN port nor the 75m cable, as plugging it in my desktop or laptop works fine. I find it hard to believe that 6 separate routers would break or have a faulty WAN port at the same time, so I'm really all out of ideas.