After more than a year, I tried again to debug this problem. I got to the root of the issue's code location, to some degree at least. Using current stable Nim 1.6.6.
<https://github.com/nim-lang/Nim/blob/0565a70eab02122ce278b98181c7d1170870865c/lib/system/io.nim#L620-L623> This is how deep I could get using `echo`. The binary is compiled using `wine64` and run on Windows 10. This issue only happens on Windows and only with a certain file, after some time of using (i.e. appending lines to) the file, randomly. Each line of the file contains a **valid** JSON object. The file is always readable/writable and works perfectly fine, until at some point it stops working and this error occurs. Then, I need to regenerate that file to make it work again. Until the error pops up, once again.
