Just noticed you call
Multiple times, not sure this is needed or an issue (don’t know that library).
It seems this is an I2C log device, and you use I2C also for other things, may be a conflict with the buffer being full and other I2C commands?
If you are on a Unix system (Linux, macOS) you could use the command line tools to extract the first (say) 500 characters of your file to see what’s actually in there (head -c 500 yourfile.CSV ). There is likely a way to do the same on windows.
You could also write a small arduino sketch that reads and print the first 500 bytes.
This way you’ll see if the file just lost the CR/LF at the end or if more data is missing…(I find it hard to believe only the last 2 bytes before a sync did not make it)