Hello @RubberDuck
I can confirm the shark fin like signals on my M5CoreS3. I am no I2C expert, but I think they might be marginal and so maybe just barely working on one M5CoreS3 but not on the other when talking to AXP2101. Maybe a stronger pull-up resistor might help?
BTW: I checked the I2C SCL line on an M5Core2 and it is much more rectangular, e.g. much more like I would expect it.
Thanks
Felix