I’ve had similar problems as others posting here have. To be honest when I’ve had to do symbolic math at work (usually some combination of computational geometry and PDEs), I typically fall back to maxima or Mathematica (if my collaborators also have licenses). Those systems are quite solid and very mature when it comes to symbolic work, and I never saw any value in using SymPy since I can get to maxima from Python via Sage. I will admit though: I tend to not do that since I’m usually pretty happy in maxima or Mathematica directly and don’t see a reason to complicate things with a layer of Python. I taught a course a couple years back where I tried to use sympy since we were using a bunch of other Python tools (numpy, scipy, etc...), and the sympy part felt very awkward. I think I remember showing the students maxima and Mathematica to convince them that computers really could do complex symbolic work and not to get too turned off by the Python tools.