Upgrading materials to HDRP/URP sometimes won't work

Hey,

I'm still new to Unity, but I've been trying to upgrade some of the free assets I've been finding on the asset store to HDRP and URP but sometimes a few assets materials remain pink even after clicking the "Upgrade Project Materials to URender Pipeline" and then "Reimport All" as the documentation suggests. From my understanding, this is because Unity cannot recognize this shader and has no idea how to proceed to it straight up puts it in default pink. (correct me if I'm wrong there).

Because of this sometimes I have to do some tweaking on the materials myself or even create brand new ones from scratch to try and match the original ones. As I say above I'm still new and I'm sure this is not the ideal way to apply these materials as the creator intended (especially having to create brand new ones imitating them...) could anyone help me out and let me know what I might be missing?

I'm attaching an example image on this post where we have a rock from the "Rocks and Boulders 2 Pack" that comes perfectly out of the box after upgrading to URP and then the same bush prefab from the "Yughees Free Bushes" asset, the left one having me tweaking the original material to try and make it look like the original and the right one just dragging it from my Asset folder straight into the scene. I've put a red circle in the obvious errors that I found (I know the missing material one is literally that but why is the prefab "losing" it's original material and the rock one isn't?). I have no idea what the "overlapping UVs" error is could you please kindly explain it to me? (the name suggests there's two or more UVs overlapping but I have no idea how to fix it or why it's happening)

Thank you so much for taking the time to help me. Have a nice day :)