Apparently I'm not the only one having issues with posts and SPT dissapearing. I found a post of someone over here with similar issues: https://www.splintertalk.io/@cryptostaker/my-missing-posts-in-splintertalk
As the posts are on the blockchain, they can't be gone. Appartenly the User Interface of Splintertalk was updated today which caused these bugs. Hopefully they can be fixed soon and our posts and SPT can be restored.
Anyone who has more information feel free to put that in the comments.