Block failed to accept after changing block header

[Bitcoin]

Block failed to accept after changing block header

I'm creating an altcoin for research proposal based on bitcoin v0.21.
I added two fields to the block header:

1. Address ID (bech32/base58)


2. Signature

Both fields are string type.

I'm creating new blocks by using cpuminer (solo mining). The mining is done by calling submitblock RPC call.
During the mining I'm getting the exception: Block decode failed which means that the server cannot deserialize the block.
When I'm calling submitblock RPC call, the new fields are empty.

When I'm creating a block by calling generatetoaddress RPC call, the block is accepted to the blockchain.

Source: Block failed to accept after changing block header