There’s probably two issues (assuming you’re actually streaming to a device inside your home network).
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Your home network seems to be segmented. That means there’s different independent network inside your home network.
This can happen if you have multiple routers or access points and each of them established its own subnet. If this happened by accident you should be able to configure each of the network devices connected to your main router in „bridge mode“… that means they should not assign local IP addresses on their own but let your router do that job.
If you have a Plex Pass and have segmented your network on purpose you can tell Plex which subnets belong to your home network (Settings>[Server Name]>Network>LAN network) -
Troubleshoot and fix your remote access setup… this can be a bit more tricky
The Basics of Remote Access Troubleshooting
If you don’t care about your remote access, fixing #1 should resolve the local quality issues.
If you’re actually streaming from a remote server, you only need to look at #2.
