The INCIDENT table misses indices on some columns which are foreign key references to other tables (and the table itself):

Proposed indices (oracle):
create index ACT_IDX_INC_CAUSEINCID on ACT_RU_INCIDENT(CAUSE_INCIDENT_ID_);
create index ACT_IDX_INC_EXID on ACT_RU_INCIDENT(EXECUTION_ID_);
create index ACT_IDX_INC_PROCDEFID on ACT_RU_INCIDENT(PROC_DEF_ID_);
create index ACT_IDX_INC_PROCINSTID on ACT_RU_INCIDENT(PROC_INST_ID_);
create index ACT_IDX_INC_ROOTCAUSEINCID on ACT_RU_INCIDENT(ROOT_CAUSE_INCIDENT_ID_);