Abnormal distance in acronym list

This is actually a feature, not a bug, as the acronym list is printed as an index. Thus tNRA and TSH get closer because they both begin with t.

You can add the option nogroupskip, described on page 160 of the documentation of package glossaries, to disable the vertical gap, and get:

documentclass[11pt]{article}

usepackage[acronym,nonumberlist,nopostdot,nomain,nogroupskip]{glossaries}
% I've also added a `nomain' to remove the warnings

makenoidxglossaries
newacronym{pcr}{PCR}{Polymerase Chain Reaction}
newacronym{trna}{tRNA}{transfer ribonucleic acid}
newacronym{mttrna}{mt-tRNA}{mitochondrial  transfer ribonucleic acid}
newacronym{melas}{MELAS}{mitochondrial encephalopathy lactic acidosis}
newacronym{tsh}{TSH}{thyroid stimulating hormone}
newacronym{acth}{ACTH}{adrenocorticotropic hormone}
newacronym{elisa}{ELISA}{Enzyme-linked Immunosorbent Assay}
newacronym{hek293ft}{HEK293FT}{human embryonic kidney 293 FT cells}
newacronym{u87}{U87}{Uppsala 87 Malignant Glioma cells}


begin{document}
    
    printnoidxglossaries
    
    TEXT:
    gls{acth}
    gls{elisa}
    gls{hek293ft}
    gls{pcr}
    gls{u87}
    gls{trna}
    gls{tsh}
end{document}