Is the homestead currently under attack? It is by design that new portals do not open while that is going on.
Where is Zixzax, at the entrance of the homestead, by the statue or the weaver? Does he have his normal dialogue or is he encouraging you to enter a portal?
The last portal opened, did you get the conversation with the spirit or demon, and return to the main section of the homestead using the portal?
If you have any unused blood stones, does Zixzax react to their use?
If Zixzax is at the start of the homestead 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.
If he is at the start but 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 party build), is to first make sure he doesn't have any help nearby; teleport him a couple times if he is close to the weaver. 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.