@michelleyyy: Please can you confirm the model number of the device you're capturing your workout data on? In the meantime, please try manually starting your workout to ensure that the data is recorded in the correct category.
I have the same issue on my Watch4 SM-R865U syncs to S21+. Health app is changing my exercise type that I manually started as "Running" to "Walking", not the most encouraging coach.
I am a constant software updater -- and this issue started for me between Jul 18, and Jul 20. My use case that has worked for years of galaxy watches, is auto-detect enabled, then manually start a running event. I guess I will try to debug that an auto-detected walk is not in progress already, and then try disabling auto-detect.
My Galaxy Watch 4 Classic, when manually starting running or walking, it is recording the opposite excerise. Just started doing this in the last week or two.