Can't Access RAX80 Settings With Safari

I have an RAX80 router and I've noticed that I can't consistently get into the router settings web page using Safari on my Mac.  

If the router was just restarted, then I can usually get settings to load in Safari using router's IP or routerlogin.net.  This only works for the first few minutes after the router is restarted.  After that, going to routerlogin.net or the router's IP using Safari on Mac results in "Safari Can't Connect to the server."

This is only a problem for Safari - I can get it to load consistently with Google Chrome, Mozilla Firefox, the iOS Nighthawk app, and even Chromium on Linux.  

This issue has been present the entire time I've owned this router, and through every firmware update that has come along since May of 2019.  I've factor-reset the router, cleared Safari caches, and even factory reset my Mac, but the issue persists.