The post I referenced was specifically for the HDHomeRun DVR UI version: 0.6.5. But this same solution worked for me for the Synology HDHomeRun DVR Manager Version:0.6.6
I specifically edited line 59 of dvrui_hdhrjson.php which on my Synology box is located at /volume1/web/HDHomeRunDVR/includes.
I had to SSH to the NAS and sudo -i to get root privileges to edit the file. That corrected the problem for me.