I have the same incubator and the first time I used it the hatch was a little late so I bumped up the temperature by half a degree and they have been on time ever since. I do not add water the first 18 days, during lockdown I increase it upto around 65% and have great hatches. It may have...
Did you monitor your air cells? It looks like you are doing well, with the hatch. Even if you are having to assist. Each batch I do helps me to make improvements so that the next batch does better.
Is it possible that your temps were a bit low as it looks like the egg sack was not absorbed. It may have just been a late death which can happen. How many left to hatch?
I also use the low humidity incubation method, I have the same incubator and run between 25 to 30% days 1 to 18. I gradually increase the humidity during lock down to about 65%. I check aircell growth days 7. 14 and 18.