Possible Bug: Alternating Usernames

[SolidCobra]

I just recently became a member of this site and whenever I log in, sometimes a bizarre username, namely, abcdefbd takes the place of my real username, SolidCobra as seen in the screenshots below.

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This baffled me because I have never seen that username before nor I have any idea how it ended up there in the first place. I also believed this to be the culprit responsible for generating the error message whenever I attempt to create a new post or thread:

Your ********** could not be processed because a security token was invalid.

If this occurred unexpectedly, please inform the administrator and describe the action you performed before you received this error.

I had to close and reopen the page, often randomly, just to get rid of this damn annoying username. If this is indeed a bug, could you please resolve it as soon as possible? Thanks for your time.