I am a severe sufferer of the same problem. In fact, it's directly related to the amount of effort I put into the meal.
When I throw something simple together: a sandwich, a simple one-pot meal, or a quick pan-fry, I can enjoy it rather easily.
When I work hard over a meal for hours or even days, I find myself completely un-interested in eating more than a bite or two of it. My appetite disappears as soon as I sit down at the table. It has nothing to do with whether or not the outcome is successful, and I do find the cooking process completely enjoyable.
The best explanation that I can muster is that my desire to eat something is linked to the psychological effort that I put into cooking it. That is, the more time I spend thinking about it, the less I'm interested in eating it.
The most recent example of this was a smoked Wagyu brisket that I tended to for the better part of a day (with a little help). It was not an intensive cooking effort (like, say, slaving over four bubbling pots on a stove), but it was an intensive psychological effort.
The outcome was quite good but I barely ate four bites.
Best,
Michael