Thanks for the feedback.
Maybe a contact problem after all.
I recently wanted to replace the external EEPROM on the motherboard for a 3D printer (the 32-bit processor of this board has no internal EEPROM, just an emulated one) with a FRAM module from Adafruit. But the module was not recognized despite the same I2C address and did not allow access. So I added an I2C EEPORM module again, which worked before.
Well, about 2 weeks ago I wanted to connect the FRAM module to an Arduino Uno, because the I needed more space for graphics and text than there is in the internal EEPROM (the FRAM module offers 32K, the internal EEPROM only 2K, me Required approx. 6K) Then the following happened: FRAM module did not keep the written data! I couldn't explain it to myself, everything was plugged in correctly and all cables looked perfect. So I ran the I2C address scanner. See there: No FRAM found. then I measured all connections on the module and to the module. Result: SDA line has no electrical connection. Then I examined it more closely, and in fact one of the two plugs on the cable (it was also a 'breadboard cable', no electrical connection to the conductor in the cable. By the way, the cable was brand new when I attached it).
After replacing the cable, the FRAM module works as expected and it now also runs on the motherboard of the 3D printer.
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