Earwigs will eat plant material and catch and eat some insects like aphids. I am not aware of them being a predator to baby birds. I would check this nestbox again in the morning to see if it is getting sprayed with irrigation water, and work on creating a band around the mounting pole which the crawling insects could not cross. I've never seen that there is any harm from it whatsoever. They like 'em.
Earwigs are herbivorous, nocturnal, and they hide in the boxes by day.
They aren't a threat at all. Wendy Guglieri Rescue, California -in the Sierra Nevada foothills 40 mi. I would be suspicious of a wet nest bottom. No, it is not. We are talking about 5 separate nestboxes, all with some amount of earwig infestation, the majority at least moderately heavy.