Yucca Rostrata advice please

Hi,

I recently repotted my Yucca Rostrata from the plastic pot it came in into an outdoor planter.

It was really healthy when I first repotted it (picture 1) but a couple of weeks later it is looking really unwell with lots of dried up brown/yellow leaves (picture 2)

The planter has a hole at the bottom and I placed some rocks in the base before adding soil to aid drainage. I used a mixture of Growth Technology Cactus & Succulent Focus Repotting Mix, and Coco & Coir Coco Grow Peat Free Compost as the potting soil. It's in a well-lit place in the garden where it gets plenty of sun and I have only watered it a couple of times, and given it one feed of fertiliser.

Can anyone please advise what I have done wrong and if I can save my lovely Yucca somehow? Should I repot again?

When I took it out of its original pot, the roots were completely covered with ants and ant eggs - I removed as many as I could but I assume these aren't really the issue given that they were already in the pot when it was looking healthy and lush.

Any advice greatly appreciated - it's making me sad to look at it like this.

Many thanks in advance.