We started seeing these recently.
ERROR 8: Undefined index: 50 at [/var/devtools/phabricator/src/applications/differential/parser/DifferentialHunkParser.php:120]
#0 DifferentialHunkParser::setNewLineTypeMap(Array of size 49 starting with: { 1 => null }) called at [/var/devtools/phabricator/src/applications/differential/parser/DifferentialChangesetParser.php:543]
ERROR 8: Undefined index: 51 at [/var/devtools/phabricator/src/applications/differential/parser/DifferentialHunkParser.php:99]
#0 DifferentialHunkParser::setOldLineTypeMap(Array of size 50 starting with: { 1 => null }) called at [/var/devtools/phabricator/src/applications/differential/parser/DifferentialChangesetParser.php:542]