Had a quick look into your logs:
You’re using a Vero which opens the media files via NFS (mediacenter stack) located on a NAS.
You say this NAS is a RPi 3B which got a new HDD.
The stalled IO stream could be any issue in the network infrastructure or is even a problem within in the NAS. I suggest you first have a look at [How To] Check Network Performance with iperf3 and verify the possible bandwidth between the Vero and the NAS.
If the bandwidth is sufficient (you can share the outputs here for help) the issue can reside on the Vero side otherwise you know for sure it is something in your network infrastructure or the NAS device itself.
Hope this helps for the first step of troubleshooting.
Addition: How is the new hard drive supplied with power? Own power supply or by the USB port of the rbp? What brand and model?