Capture card appears and disappears in the source selection menu

can you give wide specs of your whole setup, like brand/type/sort of setup etcetera

type of capture card.

in general, sometimes LOOP capture cards have to be innitialized in Hyperion as a Camera and not USB device.

you can check if live video feed is coming in without Hyperion, just install Mplayer and see if live feed is coming in on your Raspi trough USB.
if you have a live feed there ( thats not flunking out) and stable, then it has to do with settings in Hyperion probably> set USB grabber settings to static and NOT automatic.

If you don't have a live feed there then problem is probably in hardware/library>> try your grabber into a windows PC with VLC ( videolan) and see if you have a live feed. NO? then problem is probably the grabber itself. YES? look into your Raspi config.txt settings and change USB output power to maximum.

max_usb_current=1

also then update your Raspi

sudo apt-get update
sudo apt-get upgrade
sudo apt-get install git cmake build-essential qtbase5-dev libqt5serialport5-dev libqt5sql5-sqlite libqt5svg5-dev libqt5x11extras5-dev libusb-1.0-0-dev python3-dev libcec-dev libxcb-image0-dev libxcb-util0-dev libxcb-shm0-dev libxcb-render0-dev libxcb-randr0-dev libxrandr-dev libxrender-dev libavahi-core-dev libavahi-compat-libdnssd-dev libjpeg-dev libturbojpeg0-dev libssl-dev zlib1g-dev
sudo apt-get install libraspberrypi-dev

then execute in Raspi terminal with SSH or VNC>>

apt-get install mplayer
sudo mplayer tv:// -tv device=/dev/video0 -hardframedrop

note; video0 is only for device Video0 on USB, for camera devices use diffrent line

Just setting up for the first time! Looks like I have the same problem. @RCHudspeth can you pls let me know how to change automatic to USB and camera 1?