Can you click on the tree (gear cursor)? That should also trigger the dialogue with Zixzax.
Did you try in single player? Or after leaving the homestead and returning?
If you (save first) click on the NPCs with weapons drawn, can you trigger a dialogue that way, say you'll sheath the weapon and continue? What about a spell with area effect damage to provoke a reaction?
You could try teleporting Zixzax a couple times away from the other NPCs, and see if killing him would help (might reset his status when he respawns).
Please email supportdos@larian.com, with a brief description and the report.zip file (or a Dropbox or Google drive link, etc) generated by the D:OS EE Analysis Tool (for Windows). Extract the zip file somewhere and run the AnalysisTool.exe. When that loads, browse to the install folder (if it is not automatically detected), optionally run the tests first, and then generate a report (it will be saved in the same location as the Analysis Tool).
The report will contain system and game information, as well as your saved games. To reduce the file size, you can delete all but your latest save from the zip.
