Why am I getting a warning about FMT data being missing?
Logs from different autopilots and different versions of ArduPilot contain slightly different data.
At the start of your dataflash log ArduPlotter expects there to be some lines that describe the actual data in the log. These lines are known as 'FMT' data.
Without this 'FMT' data ArduPlotter cannot work out what the data within your log actually means, as it just sees just a bunch of numbers.
If you have deliberately removed these lines please re add them and then reupload your log to be able to see all of your pretty data!