I had a similar problem - the auto-renew didn’t work.
My setup had nginx proxy manager running on an unRaid box using macvlan network, and connected to unifi switching. What the problem was for me was the NPM box wasn’t able to get external network connectivity so like you I ended up reinstalling it all over again.
Problem kept happening, so in the end I just ditched it all & went CaddyV2 and (touch wood) so far no problems.
I haven’t got time to take a decent look at this right now, but will try to make time later today. But I had nightmares getting Nginx Proxy Manager to behave reliably on my unraid box - with Vaultwarden (among other things) as well coincidentally. And subsequently I ended up switching to CaddyV2 as it ended up being easier to get running and has (touch wood) so far been more stable.
I self-host a bunch of stuff and don’t bother paying for a static IP.
I just have a cron job running that checks my IP and then uses API calls to update my DNS settings. I’ve got the DNS setup with Zonomi which are a local company, it costs maybe a couple dollars a month & i’ve got 8-10 domains running at any one time.
Heh, mine’s not so different, multiple subnets - plus Wireguard :)
I don’t exactly know why but in the end it was definitely a inter-vlan connectivity problem I kept hitting. The pain was trying to prove it out as the official Nginx Proxy Manager container for unraid didn’t include anything like ping / traceroute etc.