Angels can be elect or non-elect

1 Timothy 5:21 I charge you, in the sight of God and Christ Jesus and the elect angels, to keep these instructions without partiality, and to do nothing out of favouritism.

Paul refers to elect angels, implying that there are also non-elect angels. Calvin says (Institutes 3.23.4) "The angels who have persevered in their upright state are called "elect" by Paul (1 Tim 5:21); if their steadfastness was grounded in the good pleasure of God, then the apostasy of the other angels shows these were forsaken. For that no other cause can be adduced than reprobation, which is hidden in God's secret counsel." This election must have been supralapsarian (logically before the fall) according to Geerhardus Vos. He suggests this election must be in Christ and in Christ as ruler and head (not Mediator). The elect angels did not fall but the non-elect did, according to the will and purpose of God.