I don’t believe anyone thinks that dome is cool
I appreciate it. Never heard of the cinnamon surface before..Another possibility is your seeding may have dampened off once planted. I run my seedlings in soil and this is a pretty common thing. The seeding is attacked by the bacteria and fungus and just withers and is gone. I know you are in jiffys but might be something to consider. Sprinkling a little cinnamon on the surface of the medium will stop the bad stuff from attacking the taproot
How would low humidity adversely affect a seedling?Nope not in all cases, depending on climate humidity can be extremely low in winter months, seen it first hand