Seasonic PSU does not always work.

[WellHello]

PSU model : ss-1200XP3 , Seasonic Platinum. 

Graphics card : gtx 980 20th anniversary edition , ( OC #1555mhz core , 8059 memory , but boots with factory clocks )

Processor : i7-6700k #4.6ghz , ~1.3 voltage

Mobo: Asus Hero VIII

RAM: 4x8gb ddr4 2666mhz Kingston hyper X fury Black

Others : Couple of decently powerful fans , nh-d15 cpu cooler , m.2 ssd (950 samsung ) , 2TB hdd , 2x lightning kit from nzxt

Description of problem : After installing this PSU ( older one was a 750W corsair cx , bronze rated , been hearing it is one of the worst psu's available ) , the pc randomly accepts boot. Not "randomly starting" , but it sometimes does boot when i press the power button , sometimes it does not. 95% of times when i go to sleep and shut down the pc , the next morning it is not booting. A temporary fix i've found for it to boot is to turn off the power supply from the I/O button , wait 60 secs , turn it back on , press the power button on the case. Sometimes this works the first time , but when i'm not lucky i have to do this process up to 4-5 times . My rather trusty friend to which i've turned all these years when i had a weird problem is dumb-founded. So , any advice or idea about which might be the problem ? 

To note : Pc is completely stable. The new psu allowed me to overclock my gpu much higher than before without stability issues ( although it is not that silent ). Since i've gotten it ( roughly 1 week ) I only had a single crash , that being a nvidia driver crash-recover . Everything works as intended.

[TheRandomness]

Are all the connectors seated properly?

[WellHello]

1 minute ago, TheRandomness said:

Are all the connectors seated properly?

Yes , triple-checked them. If it was a connector not being seated properly , simply turning on and off the psu wouldn't have worked.

[WellHello]

Bump ~ Problem still persists .