You appear to be in a double NAT configuration. From your logs:
Sep 01, 2020 21:18:06.590 [4528] DEBUG - PublicAddressManager: Obtaining public address and mapping port.
Sep 01, 2020 21:18:06.590 [24076] DEBUG - PublicAddressManager: Obtaining public IP.
Sep 01, 2020 21:18:06.590 [24076] DEBUG - HTTP requesting GET http://plex.tv/pms/:/ip
Sep 01, 2020 21:18:06.701 [24076] DEBUG - HTTP 200 response from GET http://plex.tv/pms/:/ip
Sep 01, 2020 21:18:06.701 [24076] DEBUG - PublicAddressManager: Got public IP from http://plex.tv: 51.x.x.x
Sep 01, 2020 21:18:09.723 [24076] DEBUG - NAT: UPnP, found device <http://192.168.39.1:5500/rootDesc.xml> with private address <192.168.39.134>
Sep 01, 2020 21:18:09.732 [24076] DEBUG - NAT: UPnP, usable device <http://192.168.39.1:5500/rootDesc.xml> with private address <192.168.39.134>.
Sep 01, 2020 21:18:09.737 [24076] DEBUG - NAT: UPnP, public address is 192.168.10.192
Sep 01, 2020 21:18:09.737 [24076] DEBUG - PublicAddressManager: got WAN IP 192.168.10.192 from router
Sep 01, 2020 21:18:09.737 [24076] WARN - PublicAddressManager: WAN IP is a private IP address
Sep 01, 2020 21:18:09.737 [24076] DEBUG - HTTP requesting GET https://51-x-x-x.38de85d1c34149ab92b28979beddf9b0.plex.direct:32400/identity
Sep 01, 2020 21:18:12.745 [24076] ERROR - Error issuing curl_easy_perform(handle): 28
Sep 01, 2020 21:18:12.745 [24076] DEBUG - HTTP simulating 408 after curl timeout
Sep 01, 2020 21:18:12.745 [24076] DEBUG - MyPlex: mapping state set to 'Mapped - Not Published'.
And:
Sep 01, 2020 23:15:06.258 [18976] DEBUG - MyPlex: updating mapped state - current state: 'Mapped - Not Published (Double NAT)'
Sep 01, 2020 23:15:07.993 [14320] ERROR - MyPlex: mapping failed due to potential double NAT configuration
Sep 01, 2020 23:15:07.993 [14320] DEBUG - MyPlex: mapping state set to 'Mapped - Not Published (Double NAT)'.
Plex detects your WAN IP as 51.x.x.x, while your router reports its public IP as 192.168.10.192. This typically occurs when you have two routers routers on your network, between you and Plex. Perhaps an ISP modem/router combo and your mesh router?
You could try correcting this in a few ways. The easiest may be to set up a DMZ on your ISP router pointing to the public IP address of your mesh router. Then, if you haven’t already, set up the port forward for TCP 32400 to your server.
There’s also the option of placing your ISP router into bridge mode, if it supports it. This will disable all of its routing functions (more or less) so that it passes all traffic to your mesh router.
Or, you could just set up your port forward on both the ISP router and the mesh router. On the ISP router, forward TCP 32400 to 192.168.10.192; on the mesh router, forward it to your server (on the 192.168.39.0/24 network?).
The information in this article may be helpful as well: