I found the solution to this from another post related to tracking image URLs:
Hi - I think that when this happens, what you have to do (anytime you have a domain like www.site.com/somethingelse) you need to go and choose "Alternate Portal Alias" setting under the control panel within the Advanced Newsletter module. Then for that you should enter an alias that is the root domain only. So... I would go and set this to be "
http://mytrooponline.org"
Making the change to the Alternate Portal Alias resolved this issue as well.
You actually don't need the "http://" in the alternate poral alias, just the root domain. In my case, I just set the Alternate Portal Alias to "mytrooponline.org" and that resolved the issue. The opt-out URL is not working properly.
Thank you.