I hope someone has an explanation for this...
I've been making little RI plaques to make as toppers for cupcakes (like the sesame street cupcakes in my photos) and it doesn't happen all the time, BUT sometimes, my plaques don't dry up with a dome/pillow effect on them. I don't get holes in them (like a crater when an air bubble escapes), but they seem to dry up with a little, "depression", if you will, in the middle of a filled space. So, I kind of get a pillow effect around the edges, only in the middle I get a "looks-like-someone's-already-placed -their-head-on-the-pillow effect"
Could it be I may be diluting the RI too much sometimes?
Hope I explained everything clearly
I think maybe you need to fill them a little thicker. The royal icing flattens some when drying.
You definitely may have added too much water to your royal.
If it's pretty humid, the royal can pick up moisture from the air and not crust over quickly enough, so a slightly thicker royal is a good idea in humid conditions.
You may have had an irregularity/wrinkle in your surface--wax paper?
You may have flooded too slowly and/or without keeping the tip buried in the icing. This causes spots of icing to be drying at different rates/times and the wetter areas will dip down next to the drier areas.