Is it a problem if I publish my thesis bearing the same title of a journal article I published previously?
No.
Your copyright should not be an issue, provided that you either are the sole owner of the copyright, or that you have provable permission of the owner/contributors to use the same name.
But on that note, names aren't easily copyrighted. There are thousands of papers, books, magazine articles, and other such that include the same kind of name as each other, and I would bet that there are one or two sharing your paper's exact name.
If anything or anyone happens to do research of their own and says anything about it, which I personally doubt will happen, but hey... Just prove that you are the owner of the document, or allowed by other contributors to use it.