Actually, after reviewing my data, this started sometime after January 28th. On or before that date, none of the activities were showing that way.  

From what app or device do you upload activities to Strava?

Garmin 630.

At first I thought maybe Garmin Connect was causing the issue, but it even does it when I directly upload the .fit file from the watch.

Hi @rdawson 

Thanks for posting about this.  If your outside run activities are uploading as "treadmill", one possibility is that no GPS data is being recorded.  If you look at the activity after you've removed the "treadmill" tag, do you see a map?  If not, that means no GPS data was recorded.  I see you're recording with a Garmin Forerunner device - I would recommend double checking the settings to ensure GPS has not been accidentally turned off.

Let us know if that works!

I never found a setting on the watch that was not what it was supposed to be.  The watch always said GPS was connected.  I ended up doing a "soft" reset on the watch though and on the next run, everything worked as it did before this problem started.

HI Jane,

Activities are being uploaded as treadmill, eventhough I am choosing outdoor walk on the watch itself.  After deleting the treadmill tag in Strava I still do not see the map. The Zepp application shows the map correctly, it looks like the GPS on the watch is working from the beginning to the end of the training. But it is still syncing to Strava without the map. Can you assist please? Is there any solution?

I have this issue also, still cant find the solution? maybe need soft reset the watch?