Weird errors when there are two misc bib entries from the same author

[Pusnow]

I have encountered weird errors when there are two misc bib entries from the same author.
It seems a bug in ACM-Reference-Format.bst file.

main.tex:

\documentclass[sigplan]{acmart}
\begin{document}
\cite{aa,bb} % --> citing only aa (\cite{aa}) does not make an error
\bibliographystyle{ACM-Reference-Format} % --> changing to plain does not make an error
\bibliography{main}
\end{document}

main.bib:

@misc{aa,
title = {aa},
author = {aa},
note = "\url{https://aa.org}"
}
@misc{bb,
title = {bb},
author = {aa},
note = "\url{https://bb.org}"
}

Error message:

! Missing = inserted for \ifnum.
<to be read again> 
                   n
l.3 \cite{aa,bb}
                
I was expecting to see `<', `=', or `>'. Didn't.

! Missing number, treated as zero.
<to be read again> 
                   n
l.3 \cite{aa,bb}
                
A number should have been here; I inserted `0'.
(If you can't figure out why I needed to see a number,
look up `weird error' in the index to The TeXbook.)

! Missing = inserted for \ifnum.
<to be read again> 
                   n
l.3 \cite{aa,bb}
                
I was expecting to see `<', `=', or `>'. Didn't.

! Missing number, treated as zero.
<to be read again> 
                   n
l.3 \cite{aa,bb}

...

[mofanv]

seems issue here. Very weird

[akosthekiss]

I am experiencing a similar issue with @online entries. Not specifying the year field seems to be a trigger. In that case, the bibliography style fills in [n.\,d.] at several places (functions format.year, output.year.check, calc.basic.label, and calc.label), which seems to make things fragile somewhere (my guess is somewhere around the labels, but that is not validated). If I manually specify year = {[n.\,d.]}, in the entries, the error is gone.

[Bulgy404]

Hey, I changed my references import from BibLateX to BibTex - that fixed the issue. I am using the Overleaf Premium function where you can directly import your references from Zotero. Maybe that helps.

[EugenioMoro]

I have had the same issue. I could resolve by adding the missing year = {[n.\,d.]}, as @akosthekiss suggested