I suspect that you’re creating a new post each time rather than updating anything, but that just a guess. I say this because your pre_save_post filter does no checking to see if the post_id is for a new post or an existing post. Your filter should only be run when the post_id is “new” or whatever value you’re using for the acf form for the new post creation see https://www.advancedcustomfields.com/resources/acf-pre_save_post/ and https://www.advancedcustomfields.com/resources/using-acf_form-to-create-a-new-post/
