Good catch. It’s difficult to comment more as the code for the functions is visible.
Can you post traceplot of the warmup iterations for some parameters?
If the problem is not due to discontinuities, then diagnostics from campfire - New adaptive warmup proposal (looking for feedback)! - might be able to tell more or at least the adapation might work better. If you try campfire, post the diagnostic results here and @bbbales2 can interpret them for you,