Eggs arent hatching

[Theeggladyox]

Hi all, just wondering if anyone could point me in the right direction of what could be going wrong! I've got 2 of the same incubators (cheapish ones), hatched some chicks out last year in this incubator and fantastic results.. put 6 bantam and 6 silkie chicks in this year and only had 3 hatch (3 were dead in the shell the rest were dud which I know can be expected) but these didn't hatch until day 24 and 25, I thought the temperature may be slightly off but in the other incubator I've got another 12 bantam eggs, currently on day 22 and no pips or signs or hatching. I've got a separate hygrometer inside and the temp is 37.6 and the humidity is 65%.

 

[muddy75]

Is your hygrometer salt-tested? Have you candled?

 

[Theeggladyox]

Is your hygrometer salt-tested? Have you candled?

I haven't candled since before lockdown but they were full when I had candled them apart from a couple of ones that didn't develop

 

[muddy75]

how did the aircells look? I would salt-test hygrometer and check for cold-spots around the incubator