Not arguing, but, based on my experience (accumulated over 30+ years

), none of the items listed should cause a freeze or lockup - at least under my understanding of the term - let's take a look at them one by one.
I'll deal with "Is JF currently enabled" & "What type of switch is being used and does it support JF" together, since they are related
As explained in the post above, JF being enabled at one end of the connection does not cause a problem and has a negligable impact on throughput - however - if JF is enabled on both ends AND the switch(es) linking the two does not support JF, there will be large numbers of dropped packets - however this will affect both http and SMB and is readily apparent in the time taken to bring up the web admin page.
Are all workstations & DNS members of the same WORKGROUP
Again - not a cause for a lockup - this would/should cause problems initially locating the drives, but once the drive has been found and attached, it should cause no further problems, and the drive should be available by it's ip address at all times (//<ip-address-of-DNS-323/Volume_1).
It should be noted that Windows search can be used to find computers or other resources when the only thing that is known is the NetBIOS name - it will search across workgroups and will even find systems in the same workgroup that are not visible in My Network Places due to the various quirks of the master browser mechanism.
Are the LAN cables purchased of (or?) home-made and what CAT are they as well as what standard 568A/B
In most cases bad cabling will not manifest itself as a lockup or freeze
requiring the device to be reset - a defective cable that allows communication will typically cause either reduced throughput - or - will cause a file transfer to fail under certain circumstances, typically small files transfer and larger files result in the connection dropping temporarily - it's been my experience that after the connection drops you can immediately reconnect and just as an example, browse the directory contents and transfer small files.
Home-made cables can cause these problems if they have been miswired - split pairs are fairly common when done by someone lacking experience, however, whether or not this causes problems is dependent on the length of the cable and perhaps how "electrically noisy" the environment is, but, typically it will not cause a lockup (see paragraph above).
What CAT - again - depends on the length and the environment - I doubt that you'll find anything less than CAT5 in the average network now and CAT5 is adequate.
TIA568A/B - irrelevant - either standard can be used as long as it is followed on both ends of the length of cable (if not a crossover cable results), yes, I am aware of the fact that it is recommended that one standard, either standard be used throughout an installation, and that switching from 568A to 568B, in a single run - for example the fixed cabling being one standard and the patch cords the other - can theoretically cause skew, you'd have to be pushing the installations to it's limits to see the results of that.
I do agree with the simplify the configuration and build from there.
Start by disconnecting the DNS-323 from the network and leaving it disconnected long enough for the freeze or lock to occur and then reconnect and see if it is accessible - the idea here is to determine if the cause is internal or external - if it's internal, reset the unit to factory defaults and reconfigure.
I'd like to suggest that you NOT save the configuration and restore it after the reset, it is possible to get a corrupt configuration file which can cause other issues (usually the web interface crashes and the shares remain available, but a complete crash of the system is not unknown).