When building a stream of Simple8b blocks the encoder acts as if they are a long continuous stream.
However, after every 16 blocks we write a control block. When a reader encounters the control block it re-initializes the decoders and default initialize the previous value to 0.
If the first Simple8b block after the control code is an RLE block it will then use 0 as the previous instead of the correct value.

To reproduce this you need a monotonically increasing value (like a counter) where we can get a RLE block for a value different than 0.