That is odd.. I'll re-run my tests to see if there are any differences connecting between the two repositories. From what I recall, the tests between repos were practically identical, apart from the content types being different. I believe IE11 or 10 may have also had this issue. I also want to note that we've attempted GraphQL queries from React to an open source Strapi CMS in the same codebase, and haven't had CORS issues, so it doesn't seem these particular browsers have issues with it.
As for why we require IOS7/IE, we're Canada's largest public library and require older browsers as some of our patrons utilize them (logically speaking, we probably have a larger percentage of older patrons with older devices than a typical online site). And as a library, it's important for us to avoid restricting access to these users.
If I still continue to have problems with one repo over another, I may also attempt to create a new repo and import all the content from the old one.
Thanks for your help.