@BobKrieger ...
I just tried creating two assignment groups in my own sandbox course, and I cannot replicate the behavior you are seeing. After I created both of these assignment groups (using the instructions outlined in How do I add an assignment group in a course?), I navigated away from the "Assignments" page. Then I returned to this page, and both assignment groups were listed at the very bottom of the page...as expected.
Have you tried clearing your browser history/cache or tried a completely different browser to see if you have a different experience? An up-to-date version of either Google Chrome or Mozilla Firefox are good choices.
If you clear your browser history/cache, I like to recommend that you then shut down your browser, re-start the browser, and then log back in to Canvas to see if anything has changed...hopefully for the better.
Beyond that, I would recommend you reach out to Canvas Support to see if they have any other suggestions for you.
How do I contact Canvas Support? - Instructure Community
Hopefully these things will help. Please keep us posted here in the Community...thanks!