I’ve had the same experience with the recent batch of candidates for a Junior Software Engineer position we just filled. Their projects looked impressive on the surface and seemed very promising.
Once we got them into a technical screening, most fell apart writing code. Our problem was simple: using your preferred programming language, model a shopping cart object that has the ability to add and remove items from the cart and track the cart total.
We were shocked by how incapable most candidates were in writing simple code without their IDEs tab completion capability. We even told them to use whatever resources they normally used.
The whole experience left us a little surprised.