SELECT on analytics task hangs when analytics_used_analysables table has enough rows

SELECT u.*, ctx.id AS ctxid, ctx.path AS ctxpath, ctx.depth AS ctxdepth, ctx.contextlevel AS ctxlevel, ctx.instanceid AS ctxinstance, ctx.locked AS ctxlocked 

FROM user u 

LEFT JOIN analytics_used_analysables aua ON u.id = aua.analysableid AND (aua.modelid = '3' OR aua.modelid IS NULL) 

JOIN context ctx ON (ctx.contextlevel = '30' AND ctx.instanceid = u.id) 

WHERE 1=1 AND u.deleted = '0' AND u.confirmed = '1' AND u.suspended = '0';

| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |

+----+-------------+-------+------------+--------+--------------------------------------------+-----------------+---------+----------------------+---------+----------+----------------------------------------------------+

| 1 | SIMPLE | u | NULL | ref | PRIMARY,user_deleted,user_confirmed | user_deleted | 1 | const | 1104191 | 5.00 | Using where |

| 1 | SIMPLE | ctx | NULL | eq_ref | cont_conins_uix,instanceid | cont_conins_uix | 16 | const,moodleorg.u.id | 1 | 100.00 | Using index condition |

| 1 | SIMPLE | aua | NULL | ALL | analusedanal_modact_ix,analusedanal_mod_ix | NULL | NULL | NULL | 81664 | 100.00 | Using where; Using join buffer (Block Nested Loop) |