Ok I tried to dig deeper in the problem, and could resolve both issues. Here’re rough hints for people with the same problem:
The partial ‘default’ is not found.
For some reason I had this code in one of my components:
data-request-update="{ default: true }"
I guess the code was simply ignored in OctoberCMS 3 and is now throwing errors.
However, there’re multiple ways to refresh some website areas, so this should be an easy fix
Variables are null in twig
All links to other pages used in components are defined as xxxPage on the page as component variable. Therefor, they’re also available as
{% set itemPage = __SELF__.itemPage %}
In OctoberCMS 3. But what I found, this is not correct within OctoberCMS 3 already.
Since I have to define a lot of pages, I created a PagesTrait which checks, if every page, required for the component, is indeed defined or if one is missing. This PagesTrait adds the value from the page as dynamic property via addDynamicProperty. Then you can call the page in the component partials like this:
$this->property("itemPage")
The call with property() is the intended way if I read it right, and the fact it worked before was never intended and is now not possible anymore due to twig not calling dynamic variables.
Maybe this helps somebody out there.
You might correct me if I’m wrong ofc 