That error comes directly from the camera and means that it isn't able to store the image, usually because it is still busy. Your instincts are correct, you could try slowing it down more but that isn't optimal.
SD cards say all sorts of stuff on them but that has little bearing their ability to write files quickly. Some kinds of cards just don't work well with the DJI cameras.
Other tips include starting with a freshly formatted card and benchmarking your card to know what settings to use.
The best way to test this is by using the Intervalometer feature in the DJI app. If it can't write a file every X seconds in there it isn't going to work in Map Pilot. Benchmarking your card so you know what it is capable of WITH YOUR CAMERA is important.
Also, we always highly suggest doing the legwork to find genuine SD cards from reputable sources. The cards that come with the aircraft always work well. We sell ones that we know work well. There is just a TON of counterfeit stuff out there.