All browsers use local machine memory (also called "cache") to store previously fetched data so it doesn't have to fetch the same data again and again. This is done to prevent unnecessary bandwidth usage and at the same time it also shows the information faster to the user - as it is local on their machine.
However, this approach backfires in some cases when the local data gets "stale". In particular during login errors, or multiple logins for the same site are used on the same machine or browser. In such cases, nothing loads in the browser window and the user will see "blank" window or a circle indicating data is still getting loaded ("...loading ...") - but nothing is displayed even after some time.
To get a fresh start and remove the stale data, the user needs to "Clear the cache" and remove the browser memory. This can be done only for the site being accessed or for everything. Process for each browser (Chrome, Safari etc.) is different and we recommend the user to simply search the process for their browser. These are well known and easy to find.
Browsers such as Chrome also provide the user to open a browser window in "Incognito" mode that essentially ignores cached data and hence stale data does not get shown to the user.
Safari uses the concept of "Private" browsing to achieve the exact same results.