iPhone connection issue

One of my users, who uses an iPhone is having the strangest issue and I can’t figure out what to even try and change or fix lol.

Setup:
Unraid server running vaultwarden in docker
vaultwarden not publicly exposed, can only connect with wireguard vpn.

Issue:
My user has an iPhone that can’t sync to the server when on their home wifi. Any other network is fine.With the VPN on it says sync failed. As far as I can tell the server doesn’t see the request.

I’ve tested other android devices even on that same wifi network and they have no issues syncing.
Heck that iPhone can sync when on mobile data with the VPN, but just not on that wifi network.

Just for some reason, THAT device on THAT wifi network on the VPN can’t connect.

Anyone have ideas on how to possibly resolve the situation?

Thanks

Do you happen to know what network your VPN/Vaultwarden are running under, and if you know the end users home network as well I would check to see if they match.

Is Vaultwarden the only resource this person accesses from your network using the VPN? Or do they access any other network storage or media player, etc?

My first guess is that the networks match, and when on their home network your VPN tells their iPhone, that your Vaultwarden server is at 192.168.0.x and the app tries to communicate to that IP address, but if their home network matches then it will simply route to a device in their own network that has absolutely no idea what to do with the information.

OMG that is actually a really good point. Because with the VPN, I have it use my rasberry pi (running pi hole) as the DNS server where I have a domain entry to my server resolve etc. That is absolutely hard coded to a local ip on my network. Which if they had a device that might cause the problem. I will at least attempt a fix for that when I visit that person.

The only reason that might not be it is, I can be on the THAT wifi with my device with the VPN on and not have problems while THEY are.

But thank you so much!