Me and my friend were running yesterday and today heroic strikes with Sunbreakers (gloves), solar grenade, song of flame, viking funeral and touch of flame and flame shield.
Every time we used together Radiance with Song of Flame it just stops grenade recharge at some point. Our super is running, but after 2-3 seconds grenades just stop regenerating for some reason, Song of Flame stops then as well while radiance is still active. This happens pretty much every time our Song of Flame clashes. The same happened to me with a random person in a strike today.
I've uploaded a clip to YT when it happens.
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A bug none the less, I believe it has to do with there being to many stacks of grenade cool down buffs. I'm sure with a "Catapult" modifier it would happen after fewer grenades.