I had what I would describe as a 90% version of this for the longest time. My mental imagery was mostly
ephemeral to the point that it may as well have not existed—attempting to picture something would give me a mental 'flash' of it, that would then instantly be replaced with darkness. Nothing would stick around long enough to permit examination.
I discovered one 'trick' to get around this: certain music would cause strong, evocative "music video" imagery to be conjured in my mind's eye for as long as I listened to it, with this being mostly directible (i.e. the emotional cues of the song were fixed, but I could constrain the imagery to anything that matched those emotional beats.) I considered myself a writer in my teenage years because I took advantage of those "synesthetic fantasias" to build up scenes and characters in a sci-fi setting of my own creation. Sadly, this ability faded with age.
More recently, I was diagnosed with Inattentive-type ADHD (and, to be clear, it was always there, rather than adult-onset; my parents just disregarded the advice of my family doctor and pretended I was neurotypical.) I began taking medication for it. My visual imagery is not ephemeral any more! I mean, it still kind of is, insofar as mental images will be lost the moment I temporarily lose focus on them—but I can now hold the images for as long as I concentrate on them.
I think I might now actually have access to the full "thought toolset" other people do, but since I developed and rely on this alternate way to go about thinking without it, I don't reach for visually-imagining as a way to do things, so it doesn't get used often.
On the other hand, I notice that, on ADHD medication, I have far fewer fleeting "unrequested" visual images. I can now imagine consciously, but it seems like the visualization capabilities of my subconscious have been switched entirely off.
Though, I do notice, if I go a day without taking my ADHD meds, the second night—when it's all washed out of my system, but my brain hasn't bounced back to producing any dopamine, so the amount in there is even lower than my baseline—I'll have really intense dreams, where the details of every scene are full of "grotesquely real" imagery, as if DeepDream were trained on Zdzisław Beksiński paintings.
This almost makes me wonder whether there's a sort of "cross-fade" potential between conscious and subconscious visualizing, controlled by dopamine. Really low dopamine: vivid dreams, no conscious visualizing. Average dopamine: meh dreams, meh visualizing. High dopamine: no dreams, vivid visualizing. (This would also fit with the observation that visual hallucinations are a symptom of mania.)