That sounds like you have a contaminated egg. Leaks are very bad and if it is happening to/has happened to all your eggs, it is probably because of a build up of pressure from bacteria thriving within the egg. Even if they don't smell bad, a beaded or leaking egg is a disaster in the incubator and is best gotten out ASAP, especially if you have other healthy eggs in there! I think opening briefly during lockdown would be less of a sin than letting an egg bomb go off.
I think the fact all the chicks are yellow is coincidental. However, if this egg and the ones in May are coming from the same parent stock, and they all went leaky at the same time rather than one going leaky and being left to spread the bad, I would question the health of the hens. If you are consistently getting contaminated eggs from those hens, it is likely that it happened before lay, or they are laying more porous eggs than not. There are lots of ways eggs can get contaminated, though, and if it is just the one egg, I would consider that it was from handling. Even as careful as we are, our bodies are practically zoos for microbes, and an egg going bad here or there is something everyone is bound to experience!
I hope your other eggs are well and behave as hoped!
As for everyone questioning the possibility of sex links, sex linked chicks are born as a result of being a first generation crossing of sex-specific color varieties. If you are concerned, I would research the ingredients for black stars. If you are making the same cross there is reason to worry, but otherwise it is coincidental!