Deluge

Each distribution has things set up slightly different. I don't use CentOS So I can't comment on the specifics of it, but I did find this guide with a quick google search.

https://rixter.com/install-deluge-on-centos-7/

You could download the .torrent again and then start it in the stopped state and do a force recheck.

It should just update if you install a newer version over top of an older version. If you want to play it safe you can make a copy of your config folder.
Mac saves its config file in .config/deluge inside of your user home folder.

The code numbers you see are actually the torrent hashes.

I think you need to set the owner/group to deluge for the mount point. It looks like /mnt/PiHDD is owned by "me". Deluge would not be able to write there.

Copy the whole .config/deluge folder to the new computer.

I have manually messed with my permissions, but mine are user and group = myusername, 755 for the deluge folder and all folders inside of it, 644 for all of the config files inside of .deluge. My other computer looks to be setup with username and group of deluge, 750 for deluge folder, 664 for the f...

Sounds like something became corrupt in one of your settings files. It could possibly be the settings file for the connection manager part. Try closing deluge and then renaming your .deluge folder. This will reset all settings to their default and see if that fixes your issues. If it does you can ei...

You need to have both installed. Sounds like some issue with the dependencies on your package manager. How are you trying to install and what OS are you using?

Sounds like maybe a permission issue when saving the profile files. Do you have write permissions there?

They are saved in your home folder, so seems odd that you would not be able to.
~/.config/deluge

It shows checking for me when I do that. Maybe it is downloading from your other client?