3 (slightly ranty) suggestions for when you are ordered to stand until everyone has received Holy Communion
A common bodily posture (Cuba)
In North America, it seems that there is a fashion (for that is the kind of thing that it is) for Bishops and priests to order the holy people of God, once they have returned to their place after Holy Communion, to remain standing until the last person has received Holy Communion. As a priest I find it baffling that some of my brethren feel the need to regiment the faithful in this way. I understand the concept of a “common bodily posture” being a sign of unity, though I think its value is exaggerated. Allowing people to kneel, sit or stand as they prefer, during a time of silent prayer after Holy Communion is not likely to cause any great spiritual disunity, whereas telling people to stand, contrary to a centuries old tradition of kneeling after Holy Communion, will cause disunity, anger and frustration.
Just to give a reference point: in the traditional Roman liturgy, on the sanctuary, the clergy in choir would kneel until the celebrant had consumed the second ablution, that is, until the Blessed Sacrament was no longer present on the altar. Knowledgeable lay people would follow this custom, but some might sit down sooner, either because of infirmity or lack of knowledge. Nobody would normally interfere.