Up until now the Lora Frame Counter, which is a security feature to prevent replay attacks, was reset every time the ATTiny rebooted (e.g. because of reset or power loss). Because of this the Frame Counter Check in the settings of the Lora devices had to be disabled, or messages after a reset wouldn't be processed by the TTN Backend.
I have now implemented a way to save the Frame Counter in the ATTinys integrated EEPROM, so it will survive resets and power loss. Because of that the Frame Counter Check can now be left enabled when using the current Firmware (starting from git commit 361f8e0b85). Please be aware that the EEPROM is reset when flashing the ATTINY, therefore you will have to reset the frame counter in the TTN-Console when reflasing a device with enabled Frame Counter Checks.
The updated firmware can be found at the usual place in my Git Repository