Import Data Azure notification is wrong for Enterprise

When importing data into a Redis Enterprise (in this case EnterpriseFlash 345 GB (1 x 345 GB)) cache, the notification in the Azure portal incorrectly says it is complete about 10 seconds after starting the process. Clearly this isn't true, and the data doesn't change.

After a few minutes it appears in Activity Log, and shows correctly that it isn't complete:

And later it completes

Server load shows no activity during this period

For reference, Azure Cache for Redis Premium instances behave as expected. While imports are just as unreliable, the notification is correct (stays spinning at the top right of the portal until it is really done), and the graphs show activity during the period.

If we look at an example of importing MUCH less data (in which case it doesn't fail) then the initial Activity Log shows like this, where the process was started at 3:37 PM:

It then seemingly doesn't do anything until 3:57 PM (20 minutes), and then over about 5 minutes processes the data. Cursor line indicates 3:37 when it should have started.

And for completeness, here is the activity log at the end once it has succeeded