A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Dear NNT,
Good day!!
I understand your concern but to my knowledge, the situation you are facing can be caused due to the SharePoint Online limits such as File/Folder names, File paths, File/Folder size limitations, or timeout connectivity issues, here are references on restrictions and limits:
Restrictions and limitations in OneDrive and SharePoint - Microsoft Support
SharePoint limits - Service Descriptions | Microsoft Learn
If the restrictions and limitations are not the problem, since the problem is related to the SMPT, I suggest you post your concern in the related Microsoft Community i.e., Questions - Microsoft Q&A to get the detailed help from the experts.
Thanks for your patience and understanding. Have a good day!!
Best Regards,
Sophia