Progress shouldn't disappear when updating in Android, unless you do the uninstall-reinstall technique when updating. That is not how you update something in Android, unless GW's signatures change for every version, for whatever reason.
EDIT: Further confirmation shows that GW does NOT change signatures every version.
And here is how you update GW on Android, if you have an old version:
Step 1: Download the newer version
Step 2: Click on the downloaded file
Step 3: Click the followup "Update" button
Step 4: Wait
Simple as that.