I can relate to your question. I too come from a software background and have had a similar set of experiences.
Even though we have had similar experiences, the underlying cause could be different. I'll share with you why I think I have had these experiences; perhaps some of my thoughts/insights might be useful to you.
You mention being interested in a variety of things: music, martial arts, software, etc. According to me all of these things -- even when they are interesting -- take a slice of your mental space. They take up space in the memory as well as the mind's computing cycles.
Software development, among all these activities is a bit different, in that it is the most stressful. Most programmers start of with a lot of passion and try to keep track of several things in their field. This is a very commendable attitude, but the rate at which stuff changes has become absolutely insane in the last few years. So IMO, regardless of passion, you are developing stress under the surface, just by having to keep up with so much. I think many of us have a silent inner fear of becoming out of touch with current knowledge. This stress works on the brain silently, till a point where something's got to break. This is not just my opinion - I have read several blog posts by developers who feel the same way.
A reason why sometimes we try to do a variety of things is because we have an achievement oriented mindset. Such a mindset unfortunately always comes with an underlying stress of not having achieved enough, and it pushes a person to achieve more, to do more. Maybe such a person cannot feel comfortable until they have spent themselves totally in trying to do things. If that is true, then fatigue and stress is bound to accumulate in the mind - and show it's impact at some point.
Now let's come to your spiritual practice. A very nice (but sometimes undesirable from a worldly perspective) effect of meditation is, that it makes you start calling out those things that are stressing you without adding any value to your life. Sure, meditation brings authentic joy, but the path to authentic joy for some/many people is through the process of calling out those things that are sapping on the spirit.
Once you start calling out things that have become part of your daily routing, suddenly everything might feel meaningless. There sets in a form of exhaustion and detachment from everything.
I am not saying this is a healthy state, but it may be part of the landscape. Even though joy and energy are some of the factors of enlightenment, not everyone experiences them right away. Very often growth happens through a tunnel of hopelessness.
This moment is perfect the way it is - just breathe -- A Zen Saying
Does this saying feel liberating to you? If it does and if you feel that you have an achievement mindset, then tempering it with a certain calm acceptance of the present might help.
Try doing fewer things and don't feel compelled to fill your day with something or the other. See if that helps. Give yourself the luxury of feeling happy even when you are not doing tasks that are in some way adding to your knowledge, etc.
I would like to respectfully disagree with the fact that joy, energy and calmness are factors which develop once someone starts meditating. Sure, they will and should develop, but nobody can say when. Different people come to meditation at different points in their life and with different backgrounds. They are certainly going to have different experiences.
IMO and with a disclaimer that it comes purely from my subjective experiences, I don't think there is anything wrong in the way you feel. Examine why you are feeling listless. Could it be that you have been over extending yourself from several years. Are you feeling tired from having to do so many things? It's possible that this is a phase, or it's possible it might be a time to introspect and find out if you are leading the kind of life that is authentic to you.
There are many mediators whose journey involves dark and difficult periods. I think it's important to be honest with yourself and also maintain a sense of humor.
I'll say, honor your journey and examine your reactions. I am sure your own self examination will show you the right way.
Great question - and an important one. Thanks for asking.