The first time I ever had sticky chicks, two had pips at the bottom where I couldn't see and they didn't make it. They were GLUED to the floor of the incubator. They were the last two, so I thought they were just slow or late quitters. When I pulled them to check viability I was horrified. Of course I went crazy trying to find info about what causes it and how to prevent it.
One popular theory seems to revolve around humidity from day 1-18. Some people blame high humidity during incubation and some people blame low humidity. It actually sounds like a lot of people are just repeating what they're reading/hearing vs. having the experience themselves to take stock of their own variables.
I've had this happen when I was experimenting with dry incubation and when I was using more traditional humidity levels. A breeder I know always keeps his humidity at 55%, which is higher than what I shoot for, but he still only has random sticky chicks. TEMPERATURE seems to be the biggest factor, hands down, for me. I have noted that this happened more often when my temps were on the higher end of the acceptable range. Bloody navels are also a symptom of higher temps, so that's where I'd focus first.
Every single egg in your incubator has its own individual variables. Some are more porous, some have thicker shells, etc. They all have different needs. We have to figure out how to fine tune our incubators for the majority of those eggs. If the majority of your chicks were sticky, I'd recommend checking your temperature first, with a very accurate thermometer. Then consider humidity. Don't give up on your incubator yet, but certainly don't trust the digital thermometer/hygrometer if it has that. I'm a big fan of the
Brinsea Spot Check thermometer. Best investment I've made this year. $24.95 was much cheaper than a new incubator! Haha!