The Exclude Broken Link Checking by URL article has the most up-to-date information on this topic.
Twitter has made changes to their platform and it now blocks DubBot's broken link checker. Our engineers have determined that this issue is coming from Twitter and other software vendors are experiencing the same issue.
To remove the error messages, we have rolled out an ignore rule for all DubBot accounts this week. The following ignore rule regex has been added:
https:\/\/twitter\.com\/(.*)
The regex only works for https:// links. If you find errors being reported for your Twitter links, please update the links to https://.
We will update this article if there are any updates to report, and we will remove the regex if/when the issue is corrected.