StepMania’s backend slowly evolved, deprecating old Lua functions. Many SM5.1 themes relied on now-removed functions like math.randomseed(os.time()) in specific ways that caused infinite loading loops or statically stuck note judgments.
: Various community members have ported and patched ITG themes to ensure compatibility with 5.1's engine, often hosted on GitHub. Where to Find Patched Themes stepmania 51 themes patched
Around 2020-2022, three major shifts rendered most classic SM5.1 themes unplayable out of the box: StepMania’s backend slowly evolved