This is something that has been made apparent to me from my students, my own experiences of taking A level physics exams and from talking with the awesome Ana from Hi-Juice.
First, I will define what I mean by a difficult question and a cryptic question.
A difficult question requires a good understanding of a difficult concept to complete. In terms of science, this would probably require complicated maths or a concept that requires knowledge of other concepts to understand.
A cryptic question may not require understanding of a difficult concept - in fact, it might be simple and straightforward. However, the language of the question obfuscates the subject knowledge required or what answer the question wants. If the question were worded differently, it would be straightforward.
After doing A level physics and talking to my students, I have realised that exam questions are more cryptic than difficult.
A level physics and chemistry do not require any maths skills above GCSE level apart from learning about logarithms in year 13. I did not find the concepts too difficult in most cases. However, on one physics paper, I completely lost the concept that the question was asking about.
I believe exam boards make cryptic questions because something or someone is preventing them from using more difficult science. However, as teachers and students get more savvy with their exam techniques and use of past papers, the exam boards have to differentiate by focusing on more and more obscure aspects of the specification (or the parts that they know that teachers don't teach so well for whatever reason) or by making cryptic questions about simple concepts.
I also expect that there will be more cryptic questions as time goes on - as more exams come out, it will be easier for students who practise all the past paper questions and be better prepared for the straightforward questions. It is always good to prepare yourself with the past paper questions, marking them and then reading the examiners' notes and taking things on board.
Answering cryptic questions is difficult because they could be about anything and they could appear to be about other things. However, there are a few things you can do:
Revise topics that aren't covered in great detail. In A level chemistry, this includes transition metals, acid anhydrides and pka. The exam boards pick up on what is taught thoroughly and what isn't and might set a cryptic question based on what is not taught thoroughly.
Read the specification - make sure you can answer a question on every point on the specification. If there is something on the specification that you haven't heard of, revise it.
Revise "case studies" that appear on the specification - they may only take up a couple of points, but exam boards like to focus on these things. A level chemistry "case studies" include air pollution, the ozone layer and cis-platin.
Good luck with cryptic questions!