I get stuck a lot too. Here are some things that work for me (or have helped), when I choose to apply them. Which I actually began doing again the other night as start of a new year.
Someone here suggested the book Effortless Mastery, and I have to admit it pushed me out of a hole. I got stuck about a third of the way through the book, but was promted to push on and I'm glad I did. It really helped me to let go of caring so much about what I was creating, and commit to just creating.
You said you've been listening to and playing a lot of different stuff. I'm surprised that hasn't helped. When I learn 4 or 5 songs in a particular genre, or from a single bassist, it often influences what comes out of me. Especially when I'm in deep. Maybe really going outside your boundaries is what you need to do. Maybe study some classical music, learn some saxaphone lines on bass, get into some old disco, learn some yes songs, country songs - whatever it takes to bust you out.
The thing that's worked best for me, and which I really need to apply now is to just commit to working at least 15 minutes a day. Regardless of what comes out. The 15 minutes almost always turns into more, and regardless - it adds up. One of the toughest things for me is when I sit and write and feel like I accomplished nothing I like. The thing is though I have to push myself past those times realizing that it's a necessary part of my process. If I don't plough through them they'll just stay there keeping me blocked. So time that seems unproductive isn't actually so. It's moving forward even if it feels it's not.
I know much of the above doesn't apply to you. Wrote for myself.

I've got work to do today and needed this primer. Good luck. I always get happy when I see people here writing. Most I believe don't. Or at least that's what I summize by the participation in these types of threads.
I"ll drop one last note. While I never really liked the book, I know many have gotten inspired and pushed through to new ground reading the bood The Artist's Way. Didn't do anything for me, but others might find it helpful.