Ok, so it's not the library. Well, I just don't know. You are using a built-in hardware I2C peripheral, right? Not some bit banged I2C. Anyway, it looks like an I2C problem to me, but I don't know what would cause it if not excess pullup resistors. It's like it's being interrupted from time to time, but that shouldn't be possible. And I don't know what the 165 stuff is all about.
Edit: When I said "not the library" I meant not the Adafruit RTC library. But it could be a problem with the Wire.h library for the 33 IOT. Or it could be problem with the 33 IOT. Others have had I2C problems with the Nano 33 IOT:
https://forum.arduino.cc/t/i2c-wire-problem-with-nano-33-iot/987526