DKIM fails in DMARC report but not when checked independantly

Question

I've been getting DMARC reports for a new domain I setup saying that the DKIM check is failing. The emails don't get blocked because I haven't set it up to be quarantined or blocked yet.

If I check the status of the DKIM, it says that the key is valid.

Why would DMARC be flagging it as a failure?

<?xml version="1.0" encoding="UTF-8" ?>
<feedback>
  <report_metadata>
    <org_name>google.com</org_name>
    <email>noreply-dmarc-support@google.com</email>
    <extra_contact_info>https://support.google.com/a/answer/2466580</extra_contact_info>
    <report_id>redacted</report_id>
    <date_range>
      <begin>1572480000</begin>
      <end>1572566399</end>
    </date_range>
  </report_metadata>
  <policy_published>
    <domain>redacted</domain>
    <adkim>r</adkim>
    <aspf>r</aspf>
    <p>none</p>
    <sp>none</sp>
    <pct>100</pct>
  </policy_published>
  <record>
    <row>
      <source_ip>redacted</source_ip>
      <count>2</count>
      <policy_evaluated>
        <disposition>none</disposition>
        <dkim>fail</dkim>
        <spf>pass</spf>
      </policy_evaluated>
    </row>
    <identifiers>
      <header_from>redacted</header_from>
    </identifiers>
    <auth_results>
      <dkim>
        <domain>redacted</domain>
        <result>fail</result>
        <selector>dkim</selector>
      </dkim>
      <spf>
        <domain>redacted</domain>
        <result>pass</result>
      </spf>
    </auth_results>
  </record>
</feedback>

Answer 1

I ended up switching my key from 2048-bit to 1024-bit and now it passes. I'm not sure at all why this is, but it works.