Inconsistency in `estimate_elastic_scattering_threshold`

[ericpre]

Describe the bug

From

To Reproduce

From the notebook https://github.com/ePSIC-DLS/Hyperspy_Workshop_2025/blob/main/EELS/EELS_finestructure_analysis_full.ipynb

import hyperspy.api as hs

s_ll = hs.load("datasets/LSMO_linescan_low_loss.hspy")
s_ll.align_zero_loss_peak()

print(s_ll.inav[:3].estimate_elastic_scattering_threshold().data
print(s_ll.inav[1].estimate_elastic_scattering_threshold().data)

gives inconsistent results. For the "same" index, the estimated threshold should be the same regardless of how it has been sliced.