here's an update on my case
the audio output had mysteriously vanished because i rewrote the SPI code including the pin init code for it, and then i've configured the chipselect pin to be controlled by the SPI peripheral on the MCU, which i thought was logical, but it turns out that this is only usable in slave mode, while in SPI master mode the chipselect pin should be GPIO and manually controlled
thus the chipselect was not actually working which explains why even the audio output stopped working - the PCM3060 was left unconfigured every time
problem solved, i got audio output working again a few days ago.. i had some days of fun working on my audio code
in the mean time i was also checking with a multimeter whether there is anything different than a flat 0V signal on the codec SDO pin (on the still desoldered R85 resistor) - nothing there, flat 0 volts
today i added code for the MCU's built-in ADCs to sample a few potentiometers, while i soldered the potentiometers, i decided to solder back the 33R resistor at R85, just in case audio input magically starts working by itself eventually
and while the potentiometer sampling worked like a charm - i lost the audio output from the codec *again*
i had not touched any related code.. the I2S signals are still there, the chipselect did not stop working.. the codec just went fully silent on me again, not even any crackles/clicks/pops during reset/configuration
