Babycurus jacksoni keep on dying :(

Hello guys, I am from Czech Republic, absolutely new to this forum, and have almost one year of scorpion keeping experience (know that it's not a lot . I hope that I don't repeat somebody's question
I was wondering why my Babycurus jacksoni constantly die.... I keep them on 2-3 inches of coco fiber in quite big tank with a lot of space, I keep humidity around 60%, mist one half of the substrate twice a week, and keep the temperature always under 30°C and cooler in the night. I also have another tank with desert species (3x Hottentotta trilineatus and 1x Androctonus bicolor) doing very well and keen on eating crickets, but I haven't had success with the "rainforest" setup.
Strangely, some (but not all by far!) of the crickets I give the Babycurus jacksoni "go insane" after some days in the tank... they run around wildly and then I find them lying on the back with spasmic movements of the legs, later they die. Looks like some kind of disease, but there is no visible fungus or parasites... After I changed the substrate and washed the tank, the problem persisted. I guess that the crickets can infect the scorpion, but I don't have any idea what the disease is
I would appreciate anybody's response, if you've had or heard about such a problem... I will have an opportunity to buy more scorpions tomorrow and I don't want them to die again, poor guys, I lost a gravid female right now, have just 2 more males now, since May 7-8 jacksonis died on me, 1-2 every month Do you think I should start using sand/peat mix instead of coco fiber? I am also thinking about putting some Heterometrus inside instead of the B. jacksonis. Any advices? Thanks a lot in advance!

Well crickets die that way. On their backs, twitching. Usually they dont live very long either. Make it hot for them and they die even faster.

Add humidity to it and it gets even hotter (feeling).

So thats pretty normal.

What I would suggest is to allow for air movement. Stale air is a silent killer.
Cannot think of much else atm.

I know that crickets don't live long, but the problem is that even nymphs die that way in my tank... And about roaches pretty the same - nymphs and adults, every day one or two with their legs up. Actually, most of the tank lid's surface is filled with a mosquito net, so that air is allowed to exchange. I also have a little fan on it, but for the size of the tank a bigger one may be appropriate, gonna think about that. Thanks!

When crickets are exposed to moisture they die.. At least they do here too. But the scorpions feel quite at ease as long as there are some dry spots too.

Try putting a thermometer in, it could be inside the enclosure it gets TOO hot.. or not hot enough.

As I said, I keep the temperature in the range, using a bulb on one side and a thermometer too. But I was thinking a lot during the afternoon now... I use coconut caps as hideouts for the scorpions (the easiest way to obtain one, they sell them all around...) and the air actually gets stale underneath them, true? I saw some pictures of others' setups and saw only pieces of bark, no caps...
Btw, the two males I still have look like having their tales already infested by a fungus

You should try placing bark slabs vertically and close together so they can hide in the spaces between them.

Oki, keep the 30c and stop misting! pure water into the tank, B.jacks like it pretty wet and they need alot of ventilation.