ATmega328 behaving differently

Hello,
so I designed a custom PCB with the processor ATmega328. First I uploaded Blink sketch via USBtinyISP (working on 5V) connected on ICSP header, just to see if the board is working and after upload it seemd working just fine. Then I unplugged USBtinyISP and plugged in microUSB to supply power, that has 3.3 V after the LDO.
FOR SOME REASON THE LED BLINKED LIKE 5x MORE FREQUENT THAN IT SUPPOSED TO WHEN WORKING ON 3.3 V.
I don’t see the reason for this behaviour, since there is no difference in code or whatsoever. The processor is designed to work from 1.8 to 5.5 V, so voltage difference should not be the problem?
Can anyone help me? Anyone ever had the same issue?

So I just uploaded the bootloader one more time and changed a few settings and then the code worked fine. So that is that.

But has anyone any idea what was causing that behaviour, beacause I still don't see the reason for that.

it seams that the start on power became a problem
so tickering up to 3,3V in more then 100ms will give a timer init problem

When you loaded the bootloader, what board type did you specify. If you selected "Uno" you'd probably have got a brown out fuse setting of 2.7 volts. If the power supply voltage was in this area, it is possible that the flashing you have described, and based on the sparse information supplied, was due to a reset cycle.

morientess97:
So I just uploaded the bootloader one more time and changed a few settings and then the code worked fine. So that is that.

But has anyone any idea what was causing that behaviour, beacause I still don't see the reason for that.

So what fiddling did you do with the settings?

morientess97:
I don't see the reason for this behaviour, since there is no difference in code or whatsoever. The processor is designed to work from 1.8 to 5.5 V, so voltage difference should not be the problem?

Which frequency are you using. At 3.3V, 16MHz is out of spec.