I have discovered a couple of bugs, using the latest release of Premiere (14.5) and AE (17.5) I am using the Beta PP (14.6.0) to replicate them, as we have rolled back to the prvious release versions.
Firstly, exporting from Premiere, the 'Set Timecode Start' tick box has no affect on the exported files timecode. If the export is done via AME the timecode is changed. As a side note. the 'Success' confirmation box seems an unnecessary piece of information and an additional keystroke before you can see your export re-imported to the project.
Secondly, and this is unclear as to wether PP or AE are the issue. We seem to have an interpretation issue with some .mogrt files, which we use exstensively. As yuo will see in the attached images, it appears certain blend modes or layer media appear to be misinterpreted or lost. The thumbnail image of each .mogrt, in the cloud library, appear correctly but once imported to PP do not appear correctly.