Very interesting... I think you have a problem apart from incubation if you only had 2 of 7 total clutches not slug-out. I would strongly recommend you check out your setup and make sure everything is 100% fine. I have had years where my females only gave me 3 clutches and I've had years where I've had 10+ clutches and I've never had a clutch go bad. Does this mean that it's impossible for that to happen? No. It happens and that's life. But to have more than 50% of your females lays slugs, something has to be off. I would double and triple check the temps of every square inch of every single enclosure with a couple temp-reading devices just to see if your having heat spikes of some sort. You could, very well, have a heat spike in the males tub causing his sperm to go bad.

Now once that issue is taken care of, I would make sure your incubation method is 100% on point before trying to incubate again. Artificial incubation (which is what the majority of us do (pulling eggs from mom)) is VERY simple! Many people often over-complicate it and make it worse than it should be. My first year breeding, I had 3 clutches. My incubator was a Coleman 120qt cooler bought at Walmart. I laid a strip of heat tape on the bottom and added a small computer fan to it. Placed my 3 egg tubs and 60 days later had healthy babies. Not a single egg went bad. The following year I upgraded to a large, single door, Coke fridge with glass front and applied the same concept. Heat tape on the back, small fan for air movement and viola 100% hatch rate. This year I'm using a Hotbox incubator because it looks nice and I wasn't able to build one, but as pretty as it is, it works the same as my previous ones.

Incubating is very simple. All you need is a box of some sort (cooler, fridge, home-built box) that will hold heat well, a heating element (heat pad, heat tape, heat cable), a small fan to move air & a GOOD thermostat to make sure temps are spot on and you will be successful. Egg tubs are also very simple. Everyone I know, myself included, uses Container Store shoe bins (any tub the closes good will work just as well) for eggs tubs. I have always used vermiculite and never had a problem. I put just as much water as I do vermiculite on a weight basis in each tub. So if I use 300 grams of vermiculite I mix in 300 grams of water. Then I bury the eggs a bit in the mix and put in the 'bator. No press & seal, no opening the tubs every 2 days for air, nothing. I literally leave them there until they hatch and are ready to put in the rack.

With all this being said, this is NOT the only way of doing things, this is NOT the only right way of doing things. This to me is the most simple way to do it and will help you learn some basics in hatching eggs. If you want to try other methods, such as, substrateless, by all means go ahead. Just do your research so you know what you're doing. This whole process is fairly simple and overthinking or stressing can hurt you more than help you. Good luck my friend!