Sounds like you have already tried most of my usual suggestions and ruled out some things.
Other possibilities you may not have tried yet:
Try another browser -- aside from ones you have used recently, preferably the latest version of a popular browser with default settings and no add-ons installed. That, or at least a private or incognito browser window. If either of those allow you to sign in, try manually clearing just your eBay cookies in your original browsers. Sometimes clearing all cookies fails to work with a corrupt cookie, and a manual deletion of just eBay cookies is much less disruptive.
If you still have issues, try temporarily disabling add-ons (though if you are able to sign in to other eBay accounts, I would not expect an add-on conflict to affect just one account, unless there is another confounding issue involved).
If you are using a bookmark to sign in, try going to ebay.com and signing in there directly. In some cases an old bookmark may not be redirecting properly, causing problems.
If you have that eBay account linked to a social media account, try signing in that way; it may have other dependencies that are not subject to your current problem.
I once had a sign-in issue that turned out to be linked to an intermittent keyboard problem. A rare key combination -- a particular shift key when used with another key -- failed to register properly. Because that particular combination really only occurred in one of my passwords, the flaky keyboard was unnoticed until I could no longer sign in on the device with that keyboard. Though you say you do not get a "does not match" error, so that is likely not your particular issue.
If switching between accounts is a problem, you may want to consider using separate browsers for each account so you can remain signed to each account at the same time and avoiding having to sign out of one to sign in to another.
