Inconsistent overfull boxes and line breaks between systems

I have two systems, one running Debian and one running Ubuntu, and both have the latest version of TeX Live installed (TeX Live 2019/dev/Debian and TeX Live 2019) from their respective repositories. A paper I’m submitting is compiling significantly differently between these two systems, with inconsistent line breaks and overfull boxes.

Just by visual inspection Ubuntu is placing significantly more space following commas. For example, in the following example document Ubuntu produces an overfull box while the line easily fits on Debian (with even enough room left over for the equation tag).

documentclass[comsoc]{IEEEtran}
begin{document}
begin{equation} A,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A,A end{equation}
end{document}

Since the output is not consistent between these systems, at least one must be in error, correct? How do I tell which has the bug? The date given on the log file is more recent on Ubuntu, but that log also says it’s using the L3 programming layer so how do I know if it’s a bug with that or not? I’ve checked that it’s not a problem with the document class as I’m using the same IEEEtran.cls on both systems.

Thanks for any help.