Is Replicating Certain Types of Medical Experiments Becoming More Difficult?

Some reasons to think yes:

Mina Bissell:
"Reproducibility: The Risks of the Replication Drive":

So why am I concerned? [About increased attention to reproducibility.] Isn't reproducibility the bedrock of the scientific process? Yes, up to a point. But it is sometimes much easier not to replicate than to replicate studies, because the techniques and reagents are sophisticated, time-consuming and difficult to master. In the past ten years, every paper published on which I have been senior author has taken between four and six years to complete, and at times much longer. People in my lab often need months — if not a year — to replicate some of the experiments we have done on the roles of the microenvironment and extracellular matrix in cancer, and that includes consulting with other lab members, as well as the original authors.

 Experiments, according to a very reasonable way of thinking, must be reproducible for their results to be valid...but that seems to mean: reproducible in principle...or eventually. Not necessarily immediately nore easily. Bissell seems to make a reasonable point: as experimental techniques become more complicated, they often become more difficult to reproduce. And if some of the techniques are a matter of esoteric know-how, then, well, if  you don't have the relevant know-how, you are much less likely to get the results.

Of course each hypothesis about why the attempt to reproduce the results failed should itself be testable, so we should be able to eventuallyfigure out in every case whether there is some relevant quirk of the lab or researchers that prevented replication. But if Bissell is right--and it sounds like it is--this can get harder and harder as the techniquest become more and more complex.