I send yourhead a report on this as well as 17 crash logs but (as per their advice on their forum post) am posting it here as well. I assume things will get sorted out eventually:-)
"After much trouble shooting yesterday I’ve gone back to Pluskit 3. On one website. I had a contact form embedded in a stacks page. I wound up just using the contact form page by itself and got rid of plus kit all together. I’m using the Volcano theme by Themeflood.
On another site. I’m embedding a Weaverpix page in a stacks page. This is a one page web site using the Codex theme by Michael David Design. For this site I needed to be able to keep using plus kit so reverted to plus kit 3. This morning I updated to plus kit 4 via rapid weaver’s update prompt and tried to publish that site again with no luck so have reverted (again) to version 3 and am now successfully publishing."
The new description of the update Pluskit4 sounds like they don’t want you using it for anything “complicated”, which, for me, is the whole reason to use it to begin with. I don’t need to embed another text page into a stacks page. I need to get these standalone pages (like weaver pix) into a stacks page. Or, replace weaver pix with a cool stacks plugin.