I've noticed that the transitions popover sometimes fails to load. The XHR request loading the transitions data shows up in Chrome as status "canceled" or in Firefox the request just doesn't have a status.
Not sure what causes this sporadic failure - perhaps it's something like if the underlying page loads faster than the popover, then something in the page causes the popover data request to be canceled?
This can be seen sporadically at URLs like /index.php?module=CoreHome&action=index&idSite=1&period=day&date=2019-09-29#?idSite=1&period=week&date=2019-09-29&category=Dashboard_Dashboard&subcategory=1&popover=RowAction$3ATransitions$3Aurl$3Ahttps$3A$2F$2Fwww.eff.org$2Fdeeplinks$2F2018$2F08$2Ftelling-truth-about-defects-technology-should-never-ever-ever-be-illegal-ever
@mfb Thanks for the report. When this happens, can you check your web server error log for the error message? Probably PHP is timing out, or exhausting memory, or something similar.
I didn't (yet) find evidence of a PHP fatal error, thus my hypothesis that the issue is on the client side, related to the page loading at the same time that the XHR request should be sent (which would not be the "normal" situation when using the matomo UI, since the page would already be loaded). However I will reverify this.