@Bastien_Siebman , thanks for the prompt!
Hi @Joas_Nicolai , welcome to the forum 
Not sure how you concluded on 75MB but the limit is 100MB in total for multiple files, and each file cannot be over 25MB. So perhaps the last file you attached went over the 100MB limit.
You can refer to point 3.3 in this post for more details and a link to the relevant product feedback request.