Incubating eggs below 20% is not good. That is the range of death during incubation.
Like Chicken canoe said, the issue with sticky chicks is more likely from shipping stress. When and egg is damaged, it takes energy to heal and that energy is taken away from proper development.
You already are doing very well with temps and humidity calibration so to get better hatches with shipped eggs:
1. Do not do a rest without incubation before putting them into the incubator. Either hand turn them or do not turn them for a day.
2. Use humidity of 30 to 35%. Do not go over 60% or below 25%. 65 to 70% during lockdown.
3. from day 8 to 18, use a cool down cycle
Try this for the next hatch and see if things go better