iPad video recording immediately stopping after starting

Try all of this to see if the issue goes away.

How much free data storage space is left on your iPad?

iDevices need to maintain, at least, 3 GBs, OR GREATER, of free data storage space.

In Settings app, General settings panel, turn OFF Background App Refresh for any apps you feel do not need constant data updating/Internet updating in the background when not using the an app OR turn OFF Background App Refresh entirely/globally for the entire device.

In Settings app, under General settings, Reset panel, at the right bottom of the list, Reset All Settings.

In Settings app (NOT from the iOS Control Panel) turn OFF Bluetooth when not using any Bluetooth devices.

Also, in general, if you want a faster IDevice, on all of my iDevices, I turn off most of the iOS motion graphics eye candy, by simply turning ON Reduce Motion in Settings app, General, Accessibilty settings.

Make sure you aren't running scads and scads of background apps in the iOS 11 Control Panel/App Switcher.

If you are, you need to quit the bulk of these background running apps by tap and hold a finger on an app window in the switcher and slide your finger upwards to quit an app. You should be able to use more than one finger to quit more than one app window simultaneously.

Also, make sure you don’t have scads and scads of active website tabs running in the web browser.

If you do, greatly reduce the amount of active website tabs your web browser.

Another thing I have to ask and inquire about, now.

Some minority of user have been turning ON and leaving ON iCloud backups continuously backing up on a constant and daily basis.

If you are one of these users, turn off iCloud backup and only turn this on to do daily backups either when you are not using your iPad for a prolonged period of time (like when you are sleeping), then turn iCloud backups OFF when actually using your iPad

OR

only perform your backups on a lesser time schedule.( like twice a week, once a week, once every two weeks, once a month, etc.).

Good Luck to You!

Have you tried a hard reset of your iPad by holding down both the Home and sleep/wake buttons simultaneously until your iPad goes to black and restarts with Apple logo, then release the buttons?