Hugo build error with HUGO_ENV variable results in errors, requires extended version of hugo

[Greenjam94]

Another topic that is related to this or reporting the same concern about not using hugo extended

Deployment not using hugo extended

As of a few days ago, netlify no longer uses hugo extended for building. With my last content update on 21.09. it still worked wonderfully. With the next content update on 30.09., however, it no longer worked. I did not change anything in the settings in netlify during this time. If I change the build image to Ubuntu Xenial 16.04, the build works without problems. But this image is only supported until 15.11. Is there a solution to this? Site: lucon.netlify.app