The powerline is probably not an issue, but it could be -- the problem here is that we don't know if it is capable of handling VLANs (unless you have looked that up and can answer that).
The problem you're experiencing is becoming more complex to diagnose because you have many variables.
- your DNS is served on your proxmox host, which means that any loss of connectivity to proxmox results in loss of dns and thus a practical loss of overall internet connectivity.
- your proxmox host needs to be configured with VLANs -- I don't know if you've done that yet, but this is key if you want to have multiple networks serviced by the single port.
- you have powerline adapters which may or may not properly pass VLANs. We can think of the powerline adapters as a switch -- the question is if they are vlan aware/compatible. See this post I wrote about VLANs and unmanaged switches. We could be running into issues here, too.
Meanwhile -- I'm going to propose a new strategy.
- Make a backup of your current configuration.
- Upgrade and reset to defaults. Your current version of OpenWrt is out of date and should be upgraded. Take the opportunity to reset to defaults to make a clean slate -- there are things in there that may be vestiges of previous efforts and/or may increase the number of variables that we have to consider (or troubleshoot) as we make changes.
- Start simple -- let's make just the lan and infra networks and get those running in general. Don't set custom DNS resolvers firewall any special firewall rules -- put the infra network in the lan firewall zone and get it running. I recommend setting it such that port 1 is tagged for both networks, port 2 is the lan, and port 3 is infra. This way you can test and prove the network.
- Remove the power line adapter from the equation. This may mean temporarily moving hardware around, but we cannot assume the powerline works with VLANs until we can verify that fact (either by its documentation or by experimental validation after the next step)
- work on your proxmox setup to ensure that the VLANs are configured on that host properly and that they are attached properly to the VMs.
- .... well... we'll continue to build out all your needed functionality, but maybe in different threads since this one really has to do with setting up the general VLANs.
Regarding upgrades: The most current version of OpenWrt is 23.05.2. You're running 22.03.5 (22.03.6 has subsequently been released), but 22.03 is going to be EOL and unsupported in ~2 months, so it makes sense to upgrade to 23.05.2.
I will be going to bed shortly, so I'll be offline for a while. Feel free to get started on this (if you agree with my order of operations), or if you want to wait, I'll should be able to help tomorrow to whatever extent our timezones overlap (I'm in California).