Nighthawk RAX-100NAS (AX5200) & Comcast issue

Recently bought this router from Best Buy and tried to set it up last night. 

I went through the installation process with the app, and when I turned the Comcast modem/router to bridge mode I completely lost all Internet access. I rebooted the modem several times, tried different connections, nothing. I put a call in to Comcast and tried to explain my problem but didn't get far. They told me to call Netgear and switched the modem back off bridge mode from their end. After that everything worked as normal.

I called Netgear and had a worse experience. They did not know what was going on either and "elevated the case". So I went into the modem's settings and turned the individual wifi radios off after the new router was up and connected, even changed the SSID to be sure I was only connecting to the Nighthawk. Everything now seems to be as it should be.

Am I missing anything by not putting this in bridge mode?