Welcome to my tail of woe.
What seems like a long time ago now, back in April, I stopped using ATmega micro controllers and settled on using ESP32 for everything. SEE: https://robs-blog.net/2020/04/08/esp32-with-dual-vfos/ . Back then, i made note that some had been reporting issues with Jason Mildrum’s Etherkit library and ESP32. I did not have this problem, thankfully. Until, today that is and now everything is broken.
I think the reason why I never had any issues like the guys have reported here: https://github.com/etherkit/Si5351Arduino/issues/66 was because my ESP32 install was a rather old one, I think it was even from before espressif took over things. And then I switched over to using PlatformIO SEE https://robs-blog.net/2020/11/27/programming-with-platformio/ and a bunch of things got updated and my old very working implementation got screwed up.
I have tried to narrow down what the issue is, but its beyond my skills as a pretend programmer. So I started to try and rule things out. Its not an actual hardware issue, because other I2C things all work fine. and I can get the SI5351 to work using other libraries, like the one from Adafruit and the one I am now using above from Pavel Milanes SEE: https://github.com/pavelmc/Si5351mcu . So after losing days screwing about with this and chasing my tail, I now get to go and rewrite a whole bunch of code that no longer works. So the crap on my bench actually works again.
So tonight, i want to get the code working on the WSPR brick again so that tomorrow I can fix the PA i destroyed and then get it on the air over the Xmas/New Years break and ro also get the receiver thats part build on the protoboard working also. Cant make a receiver without a bloody signal source LOL. No family for Xmas this year because of covid. So tomorrow I will work on stuff in my office.
Go me, I got this one working in pretty quick time. I am actually rather happy now. One more to do for the VFO on the protoboard and