SEP clients not updating

Hi There

We have run into a issue on a customers estate, more than half the client have stopped updating, im talking 3000 machines.

if we push the client from the SEPM console it installs succesfully but does not update, it fails, if we manually remove the client from the machine, reinstall and load the syslink file it works.

We have picked up there are multiple machines with the same IPS as DNS is a mess and they do not have DNS scaveging enabled. Could this be causing the issue ?

What could be causing this as i cannot install the SEP client manually on 3000 machins., they also have GUPS at each site. The GUPS are connecting to the SEPM console fine.

All help will be greatly appreciated.