ActionA, thanks for taking the time to post this.
I apologize for not looking hard enough, but now I found this thread and this that describe/question the same effect. It seems MySQL requests are the root cause, not samba/nfs. I 'm going to try the suggested workaround of disabling the “Recently Added” widget.
The other suggestion of moving MySQL DB out of the NAS solution and into RPi is also interesting and more elegant.