The return value of eth.getBlock, without mixHash field, results in false missing mixHash in JSON block header

Help Me
#1

I use ETC’s Ethereum Classic Geth 5.4.1 client

The return value of eth.getBlock, without mixHash field, results in false missing mixHash in JSON block header

Excuse me, why does ETC’s geth lose this mixHash field? I need it very much, thank you.