As it can be seen on any text instance using ats-be on the "ATS Instance Drilldown" grafana dashboard, these instances are experiencing broken connections against origin servers.
The errors causing broken connections are being logged in /var/trafficserver/error.log and they look like this:
vgutierrez@cp5007:/var/log/trafficserver$ fgrep BAD_INCOMING_RESPONSE error.log |head -1 20191028.15h06m23s CONNECT:[0] could not connect [BAD_INCOMING_RESPONSE] to 10.2.2.1 for 'https://appservers-rw.discovery.wmnet/wiki/Special:EntityPage/Q170564' vgutierrez@cp5007:/var/log/trafficserver$ fgrep CONNECTION_CLOSED error.log |head -1 20191028.13h50m20s CONNECT:[0] could not connect [CONNECTION_CLOSED] to 10.2.2.1 for 'https://appservers-rw.discovery.wmnet/wiki/Special:%E7%9B%91%E8%A7%86%E5%88%97%E8%A1%A8?hidepreviousrevisions=1&hidecategorization=1&hideWikibase=1&limit=1000&days=14&urlversion=2&peek=1&from=20191028134609&isAnon=false&action=render&enhanced=0' vgutierrez@cp5007:/var/log/trafficserver$ fgrep CONNECTION_ERROR error.log |head -1 20191028.13h53m10s CONNECT:[0] could not connect [CONNECTION_ERROR] to 10.2.2.22 for 'https://api-rw.discovery.wmnet/w/api.php?format=json&formatversion=2&errorformat=plaintext&action=query&meta=notifications¬prop=list¬filter=!read¬limit=1' vgutierrez@cp5007:/var/log/trafficserver$ fgrep INACTIVE_TIMEOUT error.log |head -1 20191028.13h56m33s CONNECT:[0] could not connect [INACTIVE_TIMEOUT] to 10.2.2.1 for 'https://appservers-rw.discovery.wmnet/wiki/Night_of_the_Living_Dead_(film_series)'
Of course some are bound to happen due to operations on the origin servers, others could be a symptom of a misconfigured service (i.e. missing public hostname on the TLS certificate SAN list)