I noticed video playback from files on my NAS copied from the SD card were stuttering. I thought the NAS was running a fast enough array, but when I copied it onto the local m.2 SSD, the 4K 30Hz video played back smoothly.
I wonder if people who were having problems with 4K video from the Mavic have a bottleneck somewhere preventing smooth playback rather than due to the video camera.

Stuttering is a common problem in some older cell phones that don't support native 4k.  I think that's mostly due to the amount of processing necessary to down-convert 4K to 720p.  It's also been noted that some of the slower SD cards don'r work well in the Mavic, presumably due to too-slow writing speed.  What is the configuration (RAID level) and type of drives (SATA,SCSI, etc) in you NAS and what is your network speed.

Running RAID 5/BTRF with 5 drives in a Synology 1513+ with WD SE drives, and 802.1ad using dual Gigabit uplink to the switch (Netgear 16 port SmartSwitch), but connection to desktop is only single gigabit.

But the SSD is faster, being a Samsung m.2 950 Pro, and what was stuttering was smooth.

It is probably bad buffering over network. Try https://mpc-hc.org/downloads/

Im almost sure it will play smooth then.