Embarrassed to ask this, but here goes...
I just upgraded to a 2nd hand 5DMkIV (previous camera the Mk2).
Just to make sure it's OK, I set it to my old favourite settings which includes AI servo (I shoot birds a lot). The light has been 'heavy overcast' for weeks, since I got the camera, so I was just shooting out of my window for testing.

Then I watched a lot of tutorials and played with a lot of buttons ... and I did 'something' and now although I'm still on AI Servo H, the camera shoots 1 image then gives me the buSY message, and it's 3-4 seconds before I can get the next click. I put a freshly charged Canon battery in, and reformatted both cards and it's the same. Not using flash.

As AI Servo was previously working fine for continuous shooting, I've clearly hit a button or a menu item I shouldn't have. The indicator for how many images I can shoot continuously is showing as [1]. I have the CF card set to accept jpeg images and the SD card set to accept RAW files. Although apparently that that slows down the buffer 'a bit', that certainly wasn't a problem before 'whatever' I did recently.

I've tried the online manual, the Bausch 5DMkIV book and googled; I'm clearly not searching for the right thing. 

Can anyone work out the stupid thing I've done?

TIA

I don't have that camera, so I can't really offer a solution, but several articles I found in a google search were talking about the Digital Lens Optimizer or Dual pixel raw being enabled and resulting in very slow processing and a busy indicator. Is it possible those are turned on? High ISO noise optimization was mentioned in a couple as well.

The other thing mentioned was slow cards, but as you were getting decent results with those cards earlier, I doubt that's it.

Hope you can figure this out (without a reset to factory settings )

Thanks, Jo-Anne. Gold Star as always.

Seems it was the Digital Lens Optimizer, which I think I switched on, on the recomendation of one of the tutorials. I'm sure I can do without it - at least, I have until now!

I'm so glad that was useful! I like to keep my search skills sharp so this was a good way to test them

Jo Ann, you're one of the very best problem solvers that I've ever "met"� certainly in cyberspace anyway. I'm impressed by how fast you came up with that solution.

Liz is lucky to have you on this forum, as are we all.