Core 30 changed the long standing shared defaults of Core and Knots. By doing this, core triggered the BIP110 reaction to enforce the default rules that Knots preserved at the consensus level. OP_return was abandoned by satoshi, he used the coinbase transacation for his messaging anyway.

Bitcoin has always allowed arbitrary data in blocks, but there has always been a limit with the node implementations! Core tries to change Bitcoin. Knots tries to preserves it. If activated, BIP110 enforces Bitcoin.

Dont twist it buddy.