LAN Server Issues - Can See Server from one PC but not another

[fragdemuerte 1]

Need some help here. Been getting into running a DayZ server and messing around with VMs (Proxmox). We have several PCs in the house, we have two copies of the game. Here's the situation:

1. I was able to host a test server off my main desktop PC, play on it, and have another family member play on it, no problem. Ran a ton of mods and had some fun. 
2. All PCs connect via two routers that act as passthroughs and have UPNP enabled.
3. When I started testing on the VM server (separate box), I logged into steam on the VM and downloaded the DayZ server there. Started up the server, and family member (with a separate account & PC) can see and join the VM server. But, I cannot from my gaming PC where I am logged into Steam.
4. I read somewhere that Steam is a bit funny about being logged into two places and I figure that turning off Steam Client while running the DayZ server is possible. I do that and still nothing.

Not sure if this is a port issue, or a Steam ID issue. I find it really odd that family member can see and join and I cannot. I don't want to buy another copy of this game in order to run it off of a VM box. But, I'd like to keep the server up and running so I don't have to shut it down when shut down my gaming PC.

Any thoughts, please feel free to "throw them at the wall."

Edited March 31 by fragdemuerte

[fragdemuerte 1]

Update - Following these steps:

1. Wiped all Steam client data from the VM Server. Wiped all Steam cache from gaming PC. Relogged in and could not see or join the VM Server.

2. Logged in as family member Steam ID on VM Server - redownloaded all server files. Logged out of VM server Steam client, deleted client. Kept all DayZ server files.

3. Family member was able to see new server and was able to join.

4. Uninstalled all DayZ client info from gaming PC as well as all cache and logs. Revalidated the game files and erased all cache.

Still cannot see or join the server.
I believe the issue is now with networking.
I'm using two routers that are connected to my main Verizon modem/router. Both routers are set to access point, so the Verizon modem/router assigns all IP Addresses.

Gaming PC is connected to the router that is also connected to the VM box. I can only assume is that there's something in the networking setup that's stopping my gaming PC from seeing the DayZ server. Or, there's something in the VM or Server config files that's stopping me from accessing the server.

Edited March 31 by fragdemuerte