Fibers 551-553 have spurious ELG redshifts in jura

[rongpu]

Re-posting what I posted on slack: Fibers 551-553 have a large number of spurious ELG redshifts in the jura reduction while the same tiles/spectra were fine in iron, which means there is something is wrong in the jura pipeline for these 3 fibers. Other tracers are also affected (with lower redshift success rates) albeit less dramatic.

The 3 fibers are visible ("cosmic-ray-like") in the ELG redshift distributions in jura (the Y1 subset):
https://data.desi.lbl.gov/desi/users/rongpu/redshift_qa/y3_vs_y1_comparison/redshift_vs_fiber_elg_norm-jura_y1_subset.png
and for comparison the same plot for the iron reduction:
https://data.desi.lbl.gov/desi/users/rongpu/redshift_qa/y3_vs_y1_comparison/redshift_vs_fiber_elg_norm-iron.png

Below are example spectra for the 3 fibers:

Fiber 551 iron:

The same spectra in jura:

Fiber 552 iron:

The same spectra in jura:

Fiber 553 iron:

The same spectra in jura:

[rongpu]

Here are the redrock redshifts vs time (LASTNIGHT) for the 3 fibers in iron:

The same 3 fibers in jura, and it appears that there are some periods of time (e.g., since December 2023) that are not affected by the issue:

And for reference 3 different fibers in jura: