I would just water thoroughly to make sure you're giving them all the moisture they need. I have one trachy planted on the south side of my house in red lava rocks, and it does the same thing. One thing I noticed today though, it just opened a new leaf that does not seem to clamp up like the rest. Maybe it's acclimating itself? It's also working on opening another spear, so it must not be too stressed.

I agree and don't think you can overwater Trachys in summer.
They get all their water from the summer monsoon in habitat.

Do they recover by nightfall or the next morning???

That's water stress. Try using drip irrigation or a soaker hose if it gets really bad. I planted new palms as well and we've gotten less than an inch of rain for the last month and a half.

The same thing is happening to my Fortuneis! WHY!?

I only have one doing this--others fine in the same location and all recent transplants (a month or so ago). Today there was rain and it was overcast and very HUMID but it still look awful. New growth seems to be robust and am hoping it will recuperate. Looking at this one specimen I have, I bet it was grown in a very shaded environment. Leaf petioles seem very long compared to the others. So it might not have been acclimated to full, unobstructed, southern exposure. I removed some of the leaves to reduce water stress. Should I remove more leaves and only rely on the new growth coming in to be normal? Surprised to be having this problem because so far it has not been too hot and soil moisture is ABOVE average. Concerned now because temps are to start to rise into low 90's for a few days. Hardy Palm, if yours is in a container, move it into shade until it recuperates (assuming it was a recent transplant).

I guess you could remove some of the leaves if you
feel like it's growing fast enough to replace them.

I planted a C.cerifera last year that did the exact same thing.

Only the new leaves have grown out of this(folding),what
I find interesting is that,it was because of the root damage/
transplant shock(or whatever)that this one actually survived
the winter intact where as mt other "healthy"one
did not survive-crown intact.

Same thing happened with my O.Imbricata the first winter,
once it rooted in it's water storing capacity worked against it over winter!