After upgrade from EE2 to EE3, it seems some member fields are missing on exp_member_data table, which are required for EE3, but those were not generated by default on upgrade procedures, which is a major bug.
Error notice :
Undefined index: m_field_ft_11 ee/legacy/libraries/channel_entries_parser/components/Custom_member_field.php, line 120
You may fix this by adding those fields on exp_member_data table.
But Upgrade procedures should add those columns on EE3 upgrade procedures.