Hello,
If you are experiencing the issue on one computer only and not when moving the file between computers, I believe this may be due to an issue with the permissions of the drives/folders your files are located on. If you would, please ensure the file locations have the appropriate read/write permissions so that they are able to be seen by your Twinmotion file. Please see Apple's article here for more information: Change permissions for files, folders, or disks on Mac
If you continue to experience this issue after, please follow up with your existing bug report ticket or create a new ticket with us using the Contact Us button here: https://twinmotionhelp.epicgames.com
Best Regards,
Morgan