This question came up in the Online 10-day Retreat Nov 3, 2020, guided by Delson Armstrong. Day 2 was part of a daily 30 -minute discussion on the suttas, the Dhamma talk and reflections.
Slightly edited to improve readability
For some beings, when they get into Infinite Space and they're sending out the Metta, and then sending out the Compassion, that they completely sometimes bypass even Compassion and bypass Joy. If it is there for a few moments, that's fine. If it's not present, that's fine. So long as you are sending out something. Whether it is Compassion or Metta, or whatever it is in that moment - while you're experiencing Infinite Consciousness - that's okay, that's all right.
Traditionally speaking, the empathetic Joy that arises, this pure joy that arises at the ability to celebrate people's successes, and the ability to celebrate their joys, is something that can be cultivated just as an exercise in your daily life. When you see somebody happy, when you see somebody smiling, you return that generosity with the smile. You empathize with their ability to be happy, you empathize with their successes, and so on and so forth.
That's one way of cultivating in practical life. But it doesn't always need to translate into, or be connected with the sixth jhana of Infinite Consciousness. So, if that's not arising, I would not consider that to be an issue.
As long as you're radiating something, whether it's Metta, Compassion or Equanimity, that's all that really matters.
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