If a player misses the same trigger three times and we are called on last one, should we apply GL?
P.E.: Glimmervoid is on the battlefield three entyre and consecutive turns with no artifacts on his controler, it triggers each eot.

Treat this an example of this phrase, from Section 1.3 of the IPG:

Separate infractions committed or discovered at the same time are treated as separate penalties, though if the root cause is the same, only the more severe one is applied.

The root cause in this case is the same - they (both/all) forgot about Glimmervoid's trigger.

One Missed Trigger infraction, one Warning.

d:^D