Build getting x3 time slower after changing Artifact directories.

I am using teamcity 2017.1.2

Initially my teamcity server and client were running on the same machine on network drives.

The server, data and artifact directories were on the C drive. The client was on the D drive. (OS is on the C).

Build was taking around 2h and had 3Go of external artifacts (not used by the build chain).

At some point, for space purpose I had to change the artifact directory from the C drive to the D drive.

This resulted in the build is now taking 6h (so x3 more time).

Both disk have the same speed/block segment size.

Most of the time should be spent compilling various files and not copying the artifact which weight only 3Go (copy takes around 1-2 minutes when doing it manually) so I am at a loss on what is happening here.

Did I miss somehting? Did something wrong? Any tips would be much apreciated !