"APM is initialising" error

I have been using the pixhawk 2.4.8 for the last 1 year. As everyone knows as soon as we plug in power via battery or computer the board lights up and beeps.
Recently it is taking too long to start. The mission planner shows “APM is initialising” and then takes about whole 5 minutes to start and light up as usual.
I also tried re-installing the hexacopter firmware, but the problem is still there.
How can I fix this issue?

When you power the board with power module, does this problem still occurs?
Remove all other modules before doing it.