Devices in the same network can't see each other

[fdw]

I'm running Pairdrop on my local network, not open to the internet at all. It's behind a reverse proxy in a Docker network, so no ports open and running on a different host than the proxy.

I can open the page on several devices, but they don't see each other, even though they're on the same (local) network. The debug log shows

pairdrop  | ----DEBUGGING-PEER-IP-START----
pairdrop  | remoteAddress: ::ffff:10.89.0.100
pairdrop  | x-forwarded-for: 192.168.178.40
pairdrop  | cf-connecting-ip: undefined
pairdrop  | PairDrop uses: 192.168.178.40
pairdrop  | IP is private: true
pairdrop  | if IP is private, '127.0.0.1' is used instead
pairdrop  | ----DEBUGGING-PEER-IP-END----
pairdrop  | 
pairdrop  | 
pairdrop  | ----DEBUGGING-PEER-IP-START----
pairdrop  | remoteAddress: ::ffff:10.89.0.100
pairdrop  | x-forwarded-for: 192.168.178.30
pairdrop  | cf-connecting-ip: undefined
pairdrop  | PairDrop uses: 192.168.178.30
pairdrop  | IP is private: true
pairdrop  | if IP is private, '127.0.0.1' is used instead
pairdrop  | ----DEBUGGING-PEER-IP-END----

which I understand that Pairdrop takes both different IPs as private and uses 127.0.0.1 instead (which won't work).

I've seen #315 and #310, but I don't think these are the same issue.