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I have now reworked a few things.
1. I supply the VDDIO_18 pin with 1.2V (using the chips power supply)
2. Checked if the crystal oscillator is still working with 1.2V and it is.
I did not look at your schematics, but you can (and should if you want to save cost) use Vcore for 1.2V. I have all my miners converted to 1.2V this way. Also you can make the 0.8V with a simple resistor divider from the Vcore (any voltage between 0.7V and 0.95V will work in my testing). The asic draws less than 10mA on the 0.8V line.