Claim Server in a Ubuntu VM Not Working

Do you receive curl results for the following IP addresses (dig results for plex.tv in the US Southeast)?

;; ANSWER SECTION:
plex.tv.		49	IN	A	52.18.248.32
plex.tv.		49	IN	A	54.77.103.183

Or, you could run a dig on the host for plex.tv and see if you can curl those in the VM. The inability of curl to reach plex.tv is probably contributing to your issue. I’m curious to see if the bare IP addresses can be reached. If not, it could imply a routing issue.