A: Why are tardigrades not surviving "tun" state?

StemQ Notice: The following is an answer to this question

By the definition:

Tun formation represents a structural adaptation to desiccation, which acts on the permeability of their body surface. Tun formation reduces the evaporation surface and in particular removes high permeability areas of the cuticle from direct contact with the air. Tun formation has been well studied in eutardigrades that seem to be able to reduce their surface area more than heterotardigrades (Wright, 1989b), which have thick cuticular plates

Reference

Do you have the right Tardigrades to start with? It's easy to roughly identify them under a magnifier/microscope.

Further, from the same article:

In fact, his experiments carried out on M. areolatus evidenced that tuns are formed only by
active animals when desiccated at opportune conditions of relative humidity, whereas at the same
conditions anesthetized (anoxic) animals simply flatten or crumple.

Did you start with active animals?

More tardi from Wiki

I suppose that you desiccated them on a filter paper, right?
It's really important to keep them dry and (if) frozen. If the temperature is lower, it's better for them. And if it's dry - it's better for them. Don't wake them up "partially", they will lose their trehalose.

Now we came to the most important point: Tardigrades can survive almost anything, but the sudden hydration. Yes... It seems like those beasts are perfectly adapted for non-Earth environment :D
Check myths related to survival skills of tardigrades

The secret is in patience, you need to hydrate them very gently.

If you have them in leaf-litter, sprinkle the leaves gently, once every 5-10 minutes. Don't rush, you can easily kill them all. I did it once...

If you have them on filter paper you need to:

• take the small Eppendorf pipette (the "Yellow one", or even the smallest tip)
• put only one drop, to barely touch the edge of your paper
• wait until it's completely absorbed, 5-10 min, before you add the next drop (only one drop!)
• about 45 min later, the paper will be completely soaked and you will see them moving

How many of them will survive?

According to my experience, about 90% will be successfully rehydrated, but it depends...
For how long were they stored, what was the humidity, was that paper mechanically damaged (touch it gently, only the edges, mark the side where animals are).

More tardi from Wiki

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