The question of whether it is possible to communicate mystical (imaginative) experience is generally misunderstood.
I don't think it is any more difficult to communicate mystically-derived experiences than any other kind of deep, difficult, or unfamiliar experience - in that there are significant constraints to it, but it certainly can be done, and has been done almost as a matter of routine at some times and places.
The main constraints are motivation and time, although some minimum level of intellectual ability is also required.
If the person intending to receive a communication concerning spiritual or mystical matters is poorly motivated, and will not devote time and effort to understanding - then he will not understand.
But this equally applies to any kind of high level or difficult communication - a scientific or philosophical concept, music theory, aspects of language... mathematics even (mathematics is as objective and public as any knowledge - but very few make the effort to understand it - which includes solving strings of problems, to ensure that the understanding is real).
Of course, the communicator may also need to make considerable efforts to ensure that what he says or writes is clear accurate, well structured - and some don't have this ability - but most people can communicate what they know, given sufficient time and motivation on both sides.
It was by this means that mystical knowledge, spiritual experience, has been communicated in the past - for example by Holy Men of many types. The system is apprenticeship - that is, prolonged and close contact between Master and apprentice, in a wide range of situations - that Master knowing, and wishing to transmit that knowledge; that apprentice wishing to learn.
This works, this is effective; and has been the basis of spiritual traditions in Christianity (especially the Eastern Orthodox church, also among Western Catholics), as well as the various Buddhist Hindu traditions.
It is only since apprenticeship, and especially spiritual apprenticeship, has broken-down and all-but died-out in the West that people have developed the idea that mystical knowledge is untransmissible.
But to claim that spiritual/ mystical knowedge is incommunicable is like someone of modest intellectual ability claiming that the subject of mathematics is untransmissible; because he cannot be bothered to dedicate much time or make much effort in that direction and, anyway, he does not know of any mathematicians who might teach him.
When the apprenticeship tradition is dead or broken (as ours is), then individuals who want to learn spiritual and mystical knowledge have to make even greater efforts to find out and learn for themselves than would have been the case in the past.
It is possible, but it does take a lot of time and effort - much like learning mathematics from books but without a teacher.