Random errors while compiling a large document with LuaLaTeX via Latexmk

Question

I'm working on a rather large (200 pages) document.

Once or twice a day, I get a compile error which references a line that does not exist in my code. That is, the line does exist, but the error references contents that are slightly different from what the file actually contains.

The last such error was:

! Undefined control sequence.
l.166 \subsecction
                {Max-Pooling}

Line 166 of file experiments.tex contains that exact line, but without the double c and the newline:

\subsection{Max-Pooling}

I'm using the continuous option of Latexmk. On failure, it automatically recompiles just fine after that error, without me having to change a file (!). If I clean the build dir and then rebuild, no such error occurs. I've configured Latexmk with a $failure_cmd that prints the tail of the log and so catched the eror, but I haven't been able to catch full the log.

This is not a showstopper for me since on a recompile the error always goes away: however it's quite disturbing. I'm at a loss as to how to provide more info.

I can't share the full document and wouldn't know how to provide a MWE for this issue, since it is not a deterministic error.

These are the packages I've loaded. I've also mounted the $out_dir to a RAM drive. I am using the book class and LuaLaTeX/Latexmk, on Kubuntu, TeX Live package:

texlive/cosmic,cosmic,now 2018.20180824-1 all TexLive