Recovering intermittent failure to sync?

Whilst syncing appears to have been working well within the solution I built, I have a situation whereby a number of records weren't pushed to the host from the remote client:

Changes made on day 1 - sync appeared to run OK, host data updated

Changes made on day 2 - sync appeared to run OK, data on host not updated

Changes made on day 3 - sync appeared to run OK, host data updated

I have no idea why the sync on day 2 would appear to have worked fine yet on later inspection of the data it transpires that record updates were not actually pushed to the host...

I realise the remote client can run the 'reset' script and then sync but am I not right in thinking that this would update all records on the mobile device replacing with the data from the host (i.e. losing changes made on the remote device)..? This would be far from ideal.

Can I run a similar reset script on the host – potentially only on select records – to force these to be updated the next time the remote device syncs (push to server)..?

I suggested to the client that she "manipulate" the data on the device in those records which failed to sync on day 2 so that they are then pushed to the host the next time she syncs which hopefully will solve the problem for now, but I wonder if there is a better way...?

Any help or advice would be appreciated!