The symptoms faced by customers typically include:

When the users perform normal navigation in Spira (e.g. open a testcase, go back from a testcase to the testsetlist, ...) or when they execute testcases manually, it occurs that the loading widget does not disappear anymore or that the screen stays white and nothing happens.

After about 5 minutes the white screen disappears and the testcase opens or the loading widget disappears. When the same user tries with Firefox, Safari or Chrome the system behaves normally.

The cause and solution is described in these articles:

Thanks to Patrik, one of our loyal customers for discovering this!