I came up with these results when implementing a feed-in tariff very profitable to the main grid. As you can see in the image, the transformer out was desconnected (it does not appear) so the conclusion was that a loop was generated.

I solved that by defining two different DSO, one for consumption (and consequently without transformer-out, so the feed-in is deactivated), and one for feed-in (and consequently without transformer-in, so the consumption is deactivated).
I do not think this change should be permament. I would suggest keeping the DSO as how it is now defined but have in mind this issue if something strange is detected.