Where do Sync transcoding versions get saved before transfer?

Can I ask where the transcoded files get stored (I assume temporarily) before they get sent to the sync device???

If you store your media remote from the PMS you would not necessarily want transcoded files to also go across the network…

Hoping that this is not the case and the transcoding is stored with the PMS and transmitted from there.

Also is the transfer peer to peer directly across the network… again, the speed of transmission seems so slow it’s like it is going out of the WAN and back in some how.

It is not stored on your NAS. See this support article - https://support.plex.tv/hc/en-us/articles/201972478-Where-are-sync-transcodes-stored-on-my-computer-

Neither should it leave your LAN and go through the WAN. That sounds suspicious, I would investigate the network first and make sure all is set correctly there (for example, that Guest mode or such has not been activated for the assumed sync client which is wireless).