Listen, I'm a nobody, but I know this stuff really well.
As I've found MANY times (most recently with Hertz but also Delta), there are tons of technologies that travel providers (and others) use, of which (if blocked/stopped) any can cause a site login problem.
Firewalls (less likely now), VPN's, CASB, SSPM, cookie blockers, and all sorts of stuff can screw it up. As can anti-DDoS tech from Imperva (Incapsula) (or Cloudflare or Akamai) which I found at Hertz, but it fell on deaf ears.
And yes it can vary with Edge vs. Chrome vs. Safari, even though they use the same Chromium renderer. Updates can cause a mess (i.e. Chrome 102 > 103, or 120 > 121) for no particular reason. Sometimes you can prevent "refresh" and core updates, other times you can't.

My findings on Delta today are that (1) the preference controller is throwing a 404/not found, (2) siteintercept.qualtrics.com (and many many child sites) is (are) often blocked, (3) bat.bing.com is flagged as malicious, (4) advertising sites - now used for other purposes - are stopped by tracking blockers (go-mpulse.net, secure.adnxs.com, quantummetric.com, flashtalking.com and doubleclick.net now Google)

But who the hell at Delta cares? 800-SKYMILES goes to central reservations, which is like "duh... let me connect you with IT/tech..."