Assertion when changing read position with Flac Format

After changing the next Read Position of my transportSource using a Flac Format, I occasionally reach a FLAC_ASSERT(0) when decoding the next audio block in FLAC_API FLAC__bool FLAC__stream_decoder_process_single(FLAC__StreamDecoder *decoder)

The value of decoder->protected_->state then is FLAC__STREAM_DECODER_SEEK_ERROR but I don’t have any other informations.

Any clue would be welcome. Thank you!