I tried disabling the firewall and opening Kodi, and the NextPVR was still not starting. I rebooted the Mac and checked Kodi and got the same thing - message that PVR manager was starting but nothing but a spinning circle and a 0% indicator. So I did the re-install Kodi thing over the existing, and this time the NextPVR still wouldn't start. I'm going to "uninstall" Kodi (drag it from applications to the trash), reboot, reinstall Kodi and see what I get. The logging is still on through all of this, I think.
I did the things I said I would do, and after re-installing NextPVR client is working again. Yes, they are on the same subnet; in fact they are plugged into the same network switch.
Just to update, the NextPVR client add-on not starting in Kodi after rebooting the Mac is persisting. It generally will start if I reinstall Kodi over itself and open Kodi again (but yesterday when I was doing repeated reboot-reload cycles occasionally it wouldn't start, and I'd have to uninstall Kodi, reboot, install Kodi for it to work again - this was inconsistent behavior and I don't know what the trigger was).
I realized that I hadn't set a PIN number in the NextPVR server settings and I didn't know what the default is, so I set one and put that number in the settings of the NextPVR client add-on in Kodi, but it didn't make any difference to the fail-to-start-after-reboot behavior. Shutting down the Mac firewall also doesn't make any difference.
It seems like this is probably some setting being incorrect somewhere (in Mac settings, or in Kodi or NextPVR client settings, or in NextPVR server settings) but I just don't know what it might be. I'm too new to Kodi and Mac's in general to guess. Maybe there's some service or something that doesn't automatically start on the Mac after a reboot that prevents the NextPVR client add-on from starting when Kodi is opened, but is started after Kodi is installed or reinstalled.
I don't have any time right now to continue to probe at this, but if you've had any other ideas of something I should try I'd appreciate them.
Also, in looking around the forums and the NextPVR download page I've seen reference to a client app written by sub for Macs and Apple TV, with instructions to get them from the App Store, but I haven't found them in the App Store. I believe I've also seen comments from sub that he got tired of trying to deal with Apple over the requirements for an app to be in the App Store, which I guess is why they aren't there now. I'm wondering if they might be available someplace else for direct download (like the Kodi add-on). I'm just looking for an alternative on a Mac to using and controlling NextPVR in a browser window.
The default is 0000 but when install with the GUI discovery should handle this. The PIN was not the issue in the logs so I will try on my Hackintosh. The server could of course also be blocking you but we never say RPi logs.
You might also consider Kodi 22 alpha 2 which should be available soon.
I'm going to update the Mac to the newest OS; I don't know that it will help with this problem but I'm going to have to do it sometime anyway, might as well do it now.
So I've updated to Tahoe (26.whatever) and my initial impression is that this has somehow fixed the problem with Kodi and the NextPVR client add-on. When the computer restarted after the update I opened Kodi, there was a brief (less than a second) message in the top right corner that I think said the PVR manager was starting up, and when I hovered over the TV selection on the left side all the NextPVR stuff was there on the main part of the window. I rebooted a couple of times and after each time I opened Kodi and NextPVR was there. The firewall is on, and I didn't change any other settings.
I'll try some more tomorrow; we'll see if this "fix" sticks. I'm very curious about why this was a problem in Sequoia, and what is different about Tahoe that seems to make it work.
Turns out I was only on Sequoia 15.5 which worked fine to a remote server and it was connecting fine after a reboot. To confirm I will update to 15.7.1 (macOS updates are so slow) so I can backup before going to Tahoe.