Found it. went back through your posts and found where you said it went off during lockdown. So day 18 or 19 more than likely. While chicks that are hatching can and do generate their own body heat, if your temps lowered for 8-12 hours that would would be a reasonable explanation for internal pips but failure to hatch.
I am attaching a pdf of a hatching record that I use. It allows you to record temp and humidity 3 times a day and to record weight if you so wish and or candling results. I candle on day 10 and day 18 only. I also can candle 48 eggs in under 2 minutes. To do so I bring the candler flashlight to the eggs and never take them out of the turner, I do not touch the eggs except to remove ones that are to be discarded until it is time to take them out of the turner.
Anyway, back to using the hatching record. Unless you keep records that you can look at, at a moments notice, how can you fix a problem and be consistent and be able to increase hatches. It might be my advancing years, but I can't remember the parameters or much of anything about last december's hatching. And as I make notes about hatching like if ambient humidity is higher than normal, without which it makes it harder than necessary to zero in on each current hatches needs.