It is not as likely as other problems but humidity below 25%, getting into the single digits is similar to incubating at below 97F for temps. It is a zone of death and bad hatching. You can still get some to hatch but not that manyJust to be clear are you saying that humidity possibly had something to do with embryos dying at such an early stage?
I'm not worried about the humidity right now.
I will bump it up for lockdown.
Experimenting with humidity would be to find the humidity that gives you the best hatch. That would be between 25% and 45%(I would not go below that and have used 30% as the low--works great for marans but not for dorkings for example)