pert:
Please post a link to the optiboot and instructions. I know you already solved your issue by using MightyCore but if there's an issue with the other it would be nice to try to fix it.
I took the stuff I used from: GitHub - Optiboot/optiboot: Small and Fast Bootloader for Arduino and other Atmel AVR chips
Like you say, mighty seems to have sorted it.
pert:
What do you mean by that?
eg i had various boards entries (optiboot, breadboard, attiny) in the hardware directory, the IDE doesnt seem to update these, or even alert that they may need updating.