Sibling pic03

Your spider does not look like he is per-molt, this is what you should see if he was, he's abdomen would go black and shiny and he would of become bald.

Yes.. I realize that dude... The new exo-skeleton visible under the old one.. Like I said previously, I can see its not in pre-molt.. still dont know why it wont eat though..

How long has the spider been in the container, when last did you clean it substrate/re-house him?
Spider might still going into pre-molt, that why it has stopped eating.

A spider can go for month with out eating, as long as you give her moisture and water to drink the spider will be fine.
Maybe try giving her feed in the next week.
And very small food.

Spider can be a bit stressful at times, I had G. pulchripes sling, under a cm and it did not eat for 3 months, eventually it molted out, I thought it was going to die. it had also buried itself under the substrate.

There is no relationship between an upcoming moult and a bald abdomen.
The bald bottom is due to hair flicking and only allows a better view of the underlying new skin.

L. klugi are great eaters. Either you are supplying too large an item of food or it is coming up for a moult. But variation in size had little to do with it, although It might suggest the larger one is a male.

If the abdomen is rounded and there is a water supply there is no issue