Tried the Synology support route on this and all I get is that its Apple's fault.
When using the Finder in High Sierra (nMP) we tend to crash it when doing a search on the NAS server.
The crash isn't too bad, more like a window one.
It doesn't cripple the OS or computer at least.
But I have to figure this out or be forced to have our Mac network on a Windows 10 server :P