Based on the external yolk sack, I'm going to say day 18-19. Are you sure you counted your days right? Are you sure that your thermometer is accurate? You said 'there was life yesterday'- how do you know this? It clearly didn't pip internally, which means it almost definitely didn't make it past day 19 as that is the point where their lungs begin to function and they need to pip the membrane or drown.
If you counted your days right, I would bet that your thermometer is inaccurate and reading higher than your temps actually are. This would result in 2 things- a slower development and increased moisture in the egg (even with proper humidity). You said the humidity was 70%, and I am assuming you mean during lockdown. What was it through incubation and are you sure your hygrometer is accurate?
If you think there is a possibility you miscounted days (in this case, added a week of time to your memory in which case this bird is spot on for day 18-19 death day-wise.... I know I would get dates wrong if I didn't write them on my calendar) then your conditions are probably correct and your equipment is probably functioning as it should.
