Having the same issue. I know that the Netgear firmware update handles new versions of plex, and I updated to 1.0.5.18 of the firmware, which had me excited about plex being updated, but apparently Netgear messed it up.
We need to get Netgear and Plex to work better together and keep us up to date more often. Thinking about stop using Netgear and Plex altogether. Ridiculous.
netgear fixed the issue, After I paid for the gearhead support. And log on to the router tonight july 13 2020. and the issue is resolved. got the refund from Netgear support.