In the last portal opened, did you enter and talk to the demon or spirit, then return to the main section through the portal (rather than using Rift Travel to leave the End of Time)?
Since Zixzax is standing at the start of the homestead, especially if he is urging you to check out a portal, try approaching each of the remaining inactive portals and see if that triggers a conversation with Zixzax and gets the portal activated. Try walking by and clicking on the statue, as well.
If he just has his normal dialogue, try killing him, and see if that resets his status. Teleporting him may also help (though neither will if the issue is with the NPC in the last opened portal).
The best way to kill Zixzax, if you are a high enough level (about 13, depending on your party build), is to first make sure he doesn't have any help nearby (if he was beside the weaver, it would be best to teleport him a couple times). Spread your characters out on all 4 sides of him, so he can not fireball everyone at once, and then have them take turns attacking him, so you get his health down as much as possible before triggering combat. Summons help absorb some damage (he prefers attacking party members, if he has a clear line of sight), but the weaker ones don't do much damage if he isn't stunned or knocked down (which is he is fairly resistant to, though is susceptible to tripping).
If that doesn't help, please email supportdos@larian.com, with a description of the problem and the report.zip file generated by the
D:OS support tool (for the PC version). 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. Actually, at this point I don't know if the system and game information would be terribly useful, so you could just zip your latest save and email it.
Each save is a folder in the '..\Documents\Larian Studios\Divinity Original Sin\PlayerProfiles\<ProfileName>\Savegames' folder. In Windows Explorer, right click on the save folder and select 'Send To | Compressed Folder' to zip it.