Reproducible: Always
Created attachment 617944 [details] build log
With all due respect, have you even looked at your own build log? This is failing because of invalid permissions on your file system, not because there are modules missing from the list.
@Marek Szuba well, I just did a normal `sudo emerge syncthing` and this happened, so if it's not an issue specific to the syncthing ebuild than it has to be an issue with either portage or the golang eclasses that for some reason trigger something that wants to write to my user's directory. Any idea/suggestions?
And now it's working again, no clue what has changed. If you have any idea feel free to let me know.