Light of Promise

If enchanted creature is dealt lethal damage at the same time that you gain life, it won't receive a counter from its ability in time to save it.

Wotc — June 23, 2020

Each creature with lifelink dealing combat damage causes a separate life-gaining event. For example, if two creatures you control with lifelink deal combat damage at the same time, the ability will trigger twice. However, if a single creature you control with lifelink deals combat damage to multiple creatures, players, and/or planeswalkers at the same time (perhaps because it has trample or was blocked by more than one creature), the ability will trigger only once.

Wotc — June 23, 2020

If you gain an amount of life “for each” of something, that life is gained as one event and the ability triggers only once.

Wotc — June 23, 2020

In a Two-Headed Giant game, life gained by your teammate won't cause the ability to trigger, even though it caused your team's life total to increase.

Wotc — June 23, 2020