We have sent this information to D2L, and D2L is aware of this issue in their new version. It only affects lessons that have been packaged as a .zip in D2L versions earlier than 10.3.
If you package a lesson as a .zip and put it into D2L 10.3, please select the filename.html instead of the index.html.
This allows the lesson to be viewed normally.
Please see our updated D2L guide that reflects this change: http
https://supportsoftchalk.softchalk.com/FileManagement/Download/905f3fd4afea45cb9559d359f12a2cd8atlassian.net/wiki/download/attachments/129402215/lms_brightspace_by_d2l.pdf?api=v2