The compass error isn't something wrong with the compass that you need to fix.
It's your perfectly working compass telling you that it has detected a problem.
The screen message would have said Compass Error - Move Aircraft or Calibrate Compass but because the message moves across in a small box, a lot of people only notice the word Calibrate.
Unfortunately 99% of the time, that is the wrong action.
Almost always, the correct action is to move the aircraft away from the source of magnetic interference that the compass is warning you about.
In this pic I have placed my Phantom on the car roof.
The compass is just above the steel roof and it's warning me.
If I take the Phantom away from the magnetic influence the problem goes away.
DJI advise not to calibrate the compass close to magnetic influences like cars, pipes, electric cables and reinforced concrete.
Your compass has been nagging you and you've been ignoring it.
There is magnetic interference close to where you have been launching.
So far you've just been lucky that the additional magnetic field hasn't been strong enough to cause serious problems.
Find somewhere else to launch and give your compass a good calibration in a magnetically clean area.
After that you should never need to calibrate it again.