There are ways to check if a website not displaying is a problem with your browser, or with the site itself.
Could the Page Not Work on This Browser?
“Browser incompatibility” is essentially gone on any website written recently; developers use modern coding standards or get fired. (I’m not simplifying much.) Modern browsers all work with the same HTML and CSS standards.
Browser Cache Problems
One site being down on one device, and staying down for a while, yet it displays on another device, is more likely involving your browser cache, or your browser’s script blocker and/or tracker blocker.
Your browser blocking scripts and marketing trackers, is probably helping you. You can try enabling scripts on this site, and see if that helps, and then try enabling trackers; but good sites would at least tell you what won’t work unless you turn something back on.
Think about whether you want that site running unknown scripts and gathering marketing trackers, before you enable them.
Login Might Need Scripts
Internet Problems Affect Browser Cache
A momentary glitch in the Internet (at any point between your house and your Internet provider and the company’s website server) would block the page fully loading all its components. That partial web page could remain in your browser cache.
What About Site Bugs?
A bug in the site that blocks a page from loading, would likely bring it down for all browsers, and maybe even all pages of the site.
Clearing Your Browser Cache, for This Site
You can manually clear your browser cache, but that clears the cache for all websites. Probably more than you need to clear.
Try loading the website in your browser’s Private Window (that’s the term in Firefox and Chrome, Safari has something similar) which starts downloading the entire page fresh. This will have no cache, no cookies, no “behind the scenes tokens”.
You could also wait for the error on the big corporate site to be fixed, which will then have a new timestamp for the page, and your browser will know it has to re-load the page.
For testing a single page without the cache, open your browser’s Inspector, and find the “disable cache” checkbox, to force loading all the elements of the page newly.
What About Old Browsers?
Website developers check how widely new features are accepted at sites like https://caniuse.com/?search=flexbox and easily specify fall-back solutions for browsers that don’t have the newest features yet. For example, “slightly older browsers, use columns; but if you know about flexbox, here’s how I really want it displayed”.