 <p>Your regular expression has nested quantifiers (e.g. <code>(a+)*</code>). This <a href="https://swtch.com/~rsc/regexp/regexp1.html" rel="nofollow">works well with re2</a> but <a href="http://www.regular-expressions.info/catastrophic.html" rel="nofollow">not with most other regular expression engines</a>.</p>