In my experience, if there are bubbles on the outside of the shell, you missed a crack in the shell when you set it.
Temps being too high can also certainly be a problem
Candling eggs as you set them can help prevent setting eggs with small cracks from happening.
If your eggs are in an auto turner, and it is “stuck”, you may need to take a paper towel soaked w warm water and press gently against the “stuck” side. After a few minutes, the water will soften the leaked material and allow the egg to release.
Work slowly so you don’t explode a bacteria “bomb” into the incubator and put the other eggs at risk.
If you do find a crack on a valuable egg- there are threads here on sealing cracks w candle wax and generally successful hatch results - but you need to catch it/ seal them early on.
Regarding your question about humidity...
Are you concerned that you have other issues?
You said you don’t have a way to check humidity.... which.... I suggest you correct before your next hatch. Hygrometers are not expensive and can greatly increase your hatch rates.
However.
How do you monitor your eggs?
Do you weigh them?
Do you watch the air cells?
Or...?
Have you confirmed your temps in the incubator with a secondary thermometer?
Have you had successful hatches in the past?