I will ask them again. This is what Google, Mozilla, and Apple are all telling me to do. They are telling me it is an issue with the cache on the browsers and that this is the only way to fix it until they update again. It is the personal caches that the platform and the browsers connect with each other (depending on settings chosen by the user and/or outdated defaults). The platform and the browsers have not been able to give me any other information but that. This is their last response: ...I cannot say this enough: please push your users to clean their browsers and caches completely. 99% of the time it is because a user doesn't know how to clear their caches and cookies properly. They just clean one or the other, or they don't know how to. Keep this in mind before you explore other options. And if you can, please get access to their screen so you can properly clean their caches and cookies ("All Time", NOT "Past 24 Hours" or "Past Week"), close the browser completely (most browsers still run in the background even after closing them down), restart the browser and refresh any bookmarks that may be old or outdated. This is not an issue with your site, but with the connection between caches. The 400 error IS NOT a Server-Side Error. It is a Client-Side Error. And users do not like hearing that there is something wrong with their browsers or their configurations. This bug is browser based on the client side and has nothing to do with the website. Therefore, it is a client and browser problem: "All HTTP response status codes that are in the 4xx category are considered client error responses..." "Since a Bad Request Error indicates that the request sent by the client was invalid for one reason or another, it’s entirely possible the issue stems from the clients settings. Your client may be trying to send a file that’s too big, the request could be malformed in some way (viruses, malware, browser extensions or plugins, ad-blockers, etc), the request HTTP headers could be invalid, and so forth. There are literally hundreds of things that could be the culprit at this point." "If these errors are only occuring with one or two users (and nobody else is having similar issues), this just goes to prove that it is most likely a browser-related issue."