I restart this UI test where many tests failed because of random font issues: https://travis-ci.org/piwik/piwik/jobs/71735738
The next time only 13 screenshots failed yet still many screenshots are shown here: http://builds-artifacts.piwik.org/ui-tests.master/14270.7/ Most of them with a difference of 0.00%.
When UI test artifacts are uploaded again, the initial ones should be removed.
This was not a problem in the past as the diffviewer was overwritten. It's shown correctly here but the diff doesn't work anymore (this is not related to this issue): http://builds-artifacts.piwik.org/ui-tests.master/14270.7/screenshot-diffs/diffviewer.html