kinda sick of that long-ass post discovering this so here’s a short version:
Any post you currently make via the mobile app will be completely uneditable on desktop for now.
This is no rushed job either, the editing API for these posts is also disabled – meaning XKit extensions will also fail to process them. Off the top of my head, this means Quick Tags and Tag Replacer can’t touch app-made posts.
This stupid notice has honestly been driving me crazy. I hope Tumblr re-enables the editing for these posts on the website. It sucks to be limited like this.