Major - P3 Explain v2, which is used for SBE/Bonsai queries, is not supported queries against collections with hidden indexes:
abt_calibration> db.coll.unhideIndex('a_1') { hidden_old: true, hidden_new: false, ok: 1 } abt_calibration> db.coll.aggregate({$match: {a: 10}}).explain('executionStats').explainVersion 2 abt_calibration> db.coll.hideIndex('a_1') { hidden_old: false, hidden_new: true, ok: 1 } abt_calibration> db.coll.aggregate({$match: {b: 1}}).explain('executionStats').explainVersion 1