Boot Button issue, Very rare.

This is very rare, at least for me, I can’t boot inmediatly when Mac is off, I need to unplug the AC cable, plug back, push a few seconds and when I hear a little sound inside the Mac release the button and then press again and boot, anybody know about this issue could be the startup panel?, motherboard? thanks in advance.

MacPro 2010 5.1- 2,4 8 core- 64gb ram- Radeon RX580- running Mojave.