Issue 1:
I think there is a bug if you set blog to homepage, it doesn't filter based on selected categories (in my case, that's one secondary tag)and shows EVERY post as a blog post... Haha π
It will filter correctly if you navigate from a link within flarum though (eg. discussion tag, or new sidebar link)
Edit: Issue above was caused by my SSO extension
https://discuss.flarum.org/d/21666-php-and-wordpress-single-sign-on-sso-with-optional-jwt-addon
Issue 2:
If I add a blog tag after to an existing post and then load the blog page it will fail to load and throw the below error.
mount-redraw.js:15 TypeError: this.article.firstPostId is not a function
at e.a.view (BlogItem.js:98)
at Function.a (render.js:30)
at render.js:482
at f (render.js:419)
at h (render.js:315)
at render.js:444
at f (render.js:415)
at render.js:488
at f (render.js:419)
at h (render.js:302)
Issue was caused by flarum if notifications failed to send when posting (incorrect mail driver, or pretty mail template errors) because discussion would still post even though a 500 is returned, but notification would fail to send. When this happens lastpostid of the new discussion does not get set and remains NULL. I believe that is probably a flarum core issue.
Big thanks to @luceos and @JasperVriends for helping me track these down.