I am here! I don't know Postie so maybe I am wrong. It may be caused by a known issue of the current version of Polylang. The filters are added quite late in the process in a 'wp' hook and this step is never reached when doing a wp-cron.
Hopefully there is no problem when the language is set from the content (as posts urls are not modified) but it arises when adding the language code to all urls (in that case, it is impossible to find the right post url if Polylang has not done its job).
The situation should be improved with the current development version (not intended for production site yet).