That definitely sounds like your humidity is too high! Are the hatched chicks fluffing up? I'd keep ventilation open for sure, as far as I know it's not supposed to be reduced even during lockdown because of how important oxygen is to be new chicks. But I suppose your mileage may vary! I had to help out both of my chicks because the bator was opened to help my girl who had been pipped for well over 24 hours (just dampened her membranes a bit and removed a part of the shell she had been bashing her beak against for 16 hours!) and she unzipped and was out in about 2 hours. Her membranes were brown though. Then I had another previously thought unviable egg that was 3/4 of the way through the zip process at that point (of helping) that then got stuck for 12 hours... Shrink wrapped in less than 30 seconds.

so I helped her finishing zipping and she kicked her way out in about 15-20 minutes. She was also malpositioned and had zipped around the middle of the egg instead of the top!