I usually start by eliminating things from the problem to help simplify the overall troubleshooting exercise. I'd start with the WiFi because I've seen it be the source of problems more times than I'd like to admit. You can use tools such as PingPlotter (free for basic use).
NOTE: I generally just keep this running all day long, the vertical red bars are when I encountered network drops between myself and the WiFi access point.
There are other methods I'll use to do something similar to this, For example you can use the terminal application
mtr which I highlight here as well - How does MTR (run with TCP protocol) calculate the loss rate?]3.
If you find you're having issues and have the ability to use Ethernet instead, you can try switching to a physical Ethernet connection to see if the problem goes away or is mitigated.
If you've progressed past eliminating the WiFi as the problem, look next to the NAS storage connection that the macOS systems are using to communicate with the NAS.
Here you'll want to see what protocol is being used to establish the connection. Is it Samba (SMB), is it NFS or is it something else. Each of these can be problematic in their own unique ways. If you find it's one of these, then understand the stack of software that is constructing this connection from your client Macs to the NAS and verify they're using the latest versions and dig into any logs they may provide.
I can go on but this should get you started in the general direction.