help, is my egg ok ?

I am new to the forum, and new to breeding, and would really like some help.
I have a 4 week old egg, that was fertile, but looked at it yesterday and the side seems to be collapsing. I candled it, not very successfully, I couldnt see much, meaning it didnt light up well inside, but I did get some orange light. Whats happening ?
I have it in perlite and water, in a tupperware box. that is also placed in a plastic storage box, with a heat mat and thermostat, set at 82 f.
I also have 2, 5 day old eggs, both fertile, in another tupperware box in the home made incubator.
I open the tupperware oxes once a week, for air exchange and to keep an eye on the eggs.
What am I doing wrong ?
Why do the collapse this late on ? Is it normal ?
I'm a little worried because it was doing so well, until now

Ok so candled my egg again today, I can now see nothing lit up inside, no yellowing , red or anything, there is no light getting through it at all !
It is only collapsing slightly on the side, there is no mould, and no discolouration of the egg. Has an egg ever been known to hatch as early as nearly 5 weeks ?

What's your humidity inside the incubator? The eggs require 80%+ humidity, a drop in humidity levels could cause your eggs to dent. Yes there's always a chance your egg is no good or is infertile, but you don't want to give up until it deflates or molds.

An egg can hatch at 5 weeks if you are incubating for male around 89 degrees. I've hatched one a couple of months ago at 89 degrees and it took 34 days. But if you are incubating at 82 degrees for females, then it would take longer. My female at 82 degrees hatched after 53 days.

I would suggest checking your humidity levels, and make sure the temperature is fairly stable. Try to not mess with it as much, and leave it alone as much as possible. If you are incubating at 82 degrees it should take close to 2 months for it to hatch.