Activity sync issues

Just had to replace my Microsoft band 2, so i went for the Vivosport. On first glance its very nice and not a bad replacement. However I'm at my wits end with trying to get the thing to sync or receive notifications reliably.
A short activity seems to sync OK if i just leave it to sort itself out, but longer (30mins+) will not sync using connect mobile regardless of which sync button I press.

If I then use Garmin express on the PC, it reports there is nothing to sync.

I thought I would then try a manual import route, on the watch I can still see the files in the history folder, but i have failed to find these using windows explorer.

Any guidance on what to try next please?
I would also like to get the notifications to be a bit more reliable.