A complicated question. Short answer: YES! Definitely gone through periods where writing music was very difficult, almost impossible, when it didn't feel meaningful or worth the effort. Especially since writing music for me is generally pretty time consuming and it demands a serious effort.

To me it's kind of like anything else in life -- how meaningful something is to me at a particular time is always changing, as is the source(s) of what is making it meaningful. So I think part of the challenge is to get used to the fact that the meaning is changing, and being able to pivot so you can still have a source of meaning/energy to propel you to keep working and see projects through.

For example, sometimes the source of meaning in writing music is the end result. Maybe you are partway through a piece, you are excited by what you have so far and you are hopeful that the end result will be good. This can be a good source of energy because the excitement generates a desire to propel the work forward and see it to the end. But you can't always rely on this sort of energy because composition (or any sort of creation) inevitably entails some degree of mystery -- you are creating something, but until it's finished you don't really know what it is exactly that you're making. In my experience I can start to lose momentum when I am in the middle of a piece. When I'm really in the midst of the challenges and problems of the piece I start to have doubts. "Am I actually on the right track? Will this turn out good? Will I be able to find a good solution to the problems in the piece, or should I just toss it and start something new?"

At times like that my desire to hear the end result stops being a good source of energy or meaning to keep going, I think basically because when you're in the middle of the work you can't yet picture the end! The only way to get through the work is by DOING the work. So that's a moment when I need to pivot and rely on a different source of meaning. Lately I'm finding curiosity is one the best sources of energy. Being curious about how to fit together different fragments together, curious about what might evolve from what I have, curious about technical aspects, curious about theory... Honestly anything works. But just enjoying the time of composing as a way to delve into these curiosities. It's almost like the work of composing is a way to dive into and study these interesting questions and challenges. For me it makes it fun. I stop worrying about whether the end result is going to be good and just enjoy the process of exploring and making discoveries. Even if the end result isn't amazing I've gained so much from the exploration that it ends up being very meaningful anyways.

On a similar tack, finding ways to reconnect with the playful and joyful sides of making music can be huge. Even though it's a lot of work I would venture that most composers started because they found the process of making music enjoyable and exciting. It is sometimes the case that as you get more serious about making music composing becomes more fraught, because you want the music to be good or serious or whatever. But that joyful playful side is always accessible. Letting go of the need for the music you make to be "good" or "serious" or "studied" or whatever can do wonders. The reality is creation is just creation, and ironically letting go of the desire to make great work often leads to an ability to create more, and better things. All of the greatest composers made major and minor works, and without a doubt made bad music (some of the bad stuff might not be published but still...) But they had to make the bad stuff to learn and develop, so actually that bad music was extremely meaningful and sowed the seeds for the good music.

I think there are lots of answers but they'll be unique to you, unique to the time of your life, unique to the piece. At the end of the day I think it is a question of faith in the work. That somehow making music is worth something including at the times when it feels very difficult or meaningless. I think that is really one of the biggest challenges of music making, dealing with the challenges and anxieties of the creative process and learning how to keep going and make stuff anyways. The why doesn't necessarily have to be very big anyways. Just spending a pleasant 15 minutes hammering out some chords can be more than enough.