I went through this with an S7 the other day - here is a useful tip. If you go into Settings->About Phone->Baseband version, you will see an identifier. My phone is Verizon - the current version for the 04/01 security update should be something like G930VVRS4BRC3.
I had installed several updates yesterday, and thought I was in this endless loop. The updates would succeed, but there always seemed to be another. I finally looked up to see what the current baseband version was, and did a google search. Found this:
https://www.theandroidsoul.com/samsung-galaxy-s7-edge-update/
I found I was on something like the Oct 2017 security patch. So I install one more, and lo and behold, I was now on the Nov security patch. So what is clear is that it is doing the patches one at a time, and they are not cumulative. I kept going, and eventually got to the end, and there were no more updates offered. If I used Settings to check for updates, all I got was a message that "Oreo is coming soon - check back later".
All in all, I think there must have been about a dozen updates.