Weird error! Cannot add new posts while i can edit old posts? (After move from v3 to v4)

I moved my WP subdir multisite from V3 to V4 and i got this issue when i try to add new posts:

/var/www/htdocs/wp-includes/ – this folder does not exist! It was a setup from EE v3, but now the path to WP is alot different. So my guess is that this is causing the issue but i dont know how and where to fix it.

I can edit old posts just fine. I also cannot add new medias.

Also… i get this error on the main site + a couple of child sites, BUT everything works fine on a couple of other child sites.

The process of movement was… i installed EE v4 on a new server, copied the wp-content from the v3 server and i dumped the database through Mysql and switched DNS. Did i miss something?

Anyone got any ideas?

I have turned off all plugins and themes and here is the clear error again:

I have a feeling this is a serious bug with the EE v4 Wordpress Multisite installation setup.

Another error when i try to upload a media file to those broken sites:

Could not insert post into the database

Works just fine on sites where i can add new posts.

This problem is related to this:

So you can close this topic.