The roll-out of wmf11 coincides with a sharp decline in new user registrations as recorded by the MediaWiki.site.users graphite metric. This is true of the second roll-out as well, so whatever is depressing the account creation rate is still not fixed.
Related SAL entries for Jan 27th around that time (time is UTC):
21:26 logmsgbot: ori@mira Synchronized docroot and w: (no message) (duration: 02m 26s) 19:48 YuviPanda: started nfs-exports daemon on labstore1001, had been dead for a few days 19:32 mutante: stat1002 - redis.exceptions.ConnectionError: Error connecting to mira.codfw.wmnet:6379. timed out. 19:31 mutante: stat1002 - running puppet, was reported as last run about 4 hours ago but not deactivated 19:14 logmsgbot: dduvall@mira rebuilt wikiversions.php and synchronized wikiversions files: group1 wikis to 1.27.0-wmf.11 19:07 ejegg: set donation queue consumer time limit back to 90 sec 18:49 logmsgbot: jynus@mira Synchronized wmf-config/db-eqiad.php: Repool pc1006 after cloning (duration: 02m 25s) 18:48 bd808: HHVM on mw1019 still dying on a regular basis with "Lost parent, LightProcess exiting" 18:00 csteipp: deploy patch for T103239 17:50 csteipp: deploy patch for T97157