streaming from a pi3 to a pi3

Both running an up to date libre elect
Host has a western digital passport plugged into the pi3 via a hub.
Client and host has an Ethernet connection.

Any reason why movies streamed this way are occasionally freezing? Are there settings which might be doing this? Maybe “announce services” or something scanning the drive?
The pause is like 20 seconds maybe. I’m not actually doing anything else such as copying to/ from the passport while this happens