The planned hard fork of the Bitcoin Cash network has been completed, as the first block considered invalid by the older client version was noted by BitMEX Research in a tweet on Nov. 15.

Fork Monitor detected that the block at height 609,136 was considered invalid by the Bitcoin ABC 0.19.0 client. The block was accepted by Bitcoin ABC 0.20.6, confirming that the hard fork had completed as planned.

The block was mined by the BTC.com pool at 13:44 UTC, with a block-size of 0.2MB, and contained 651 transactions. Older versions of Bitcoin ABC will now either remain stuck or follow a different chain.

Simple consensus changes, but difficulty adjustment issues not addressed

As Cointelegraph previously reported, the hard fork imposed relatively simple consensus changes and was not expected to split the chain.

However, more worrying for some in the Bitcoin Cash community was the fact that the contentious Difficulty Adjustment Algorithm was not addressed. This updates the difficulty of every BCH block, based on a moving window of the last 144 blocks, or approximately 24 hours worth.

There are concerns that some miners are gaming the algorithm in order to get an advantage, with curious fluctuations in hash-rate, and volatile difficulty.