Frequency Cutoff error in preprocessing?

I'm seeing a bunch of observations raising errors that look like this:

1788491409.0804863, obs_1763234806_satp1_1111111, ['ws6', 'f090'], init_pipeline_run_error
        <class 'ValueError'>: lower freq=1 >= upper freq=0.8388319434722693  File "/global/homes/k/kmharrin/.local/soconda/20260812_0.2.5/lib/python3.13/site-packages/sotodlib
/preprocess/preprocess_util.py", line 1449, in preproc_or_load_group
    proc_aman, success = pipe_init.run(aman)
                         ~~~~~~~~~~~~~^^^^^^
  File "/global/homes/k/kmharrin/.local/soconda/20260812_0.2.5/lib/python3.13/site-packages/sotodlib/preprocess/pcore.py", line 567, in run
    aman, proc_aman = process.calc_and_save(aman, proc_aman)
                      ~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/global/homes/k/kmharrin/.local/soconda/20260812_0.2.5/lib/python3.13/site-packages/sotodlib/preprocess/processes.py", line 818, in calc_and_save
    wn_f_high = check_frequency_cutoff(wn_f_low, wn_f_high)
  File "/global/homes/k/kmharrin/.local/soconda/20260812_0.2.5/lib/python3.13/site-packages/sotodlib/preprocess/processes.py", line 792, in check_frequency_cutoff
    raise ValueError(f"lower freq={fmin} >= upper freq={fmax}")

What does this mean?

Start in sotodlib/preprocess/processes.py at check_frequency_cutoff and calc_and_save, then trace the call through pcore.py and the reported preprocessing run. Reproduce the failure with the relevant preprocessing configuration and determine why the frequency bounds are invalid. Done means the cause and expected handling are established, with a focused regression test or documented resolution.