I am running a stellar private network which is my own network. It is working fine for firing the transaction. But I have found that if I want to send transaction for particular some of accounts getting "History: Bad ledger-header history entry" but transaction is successful. After that my horizon got out of sync. My private network also running 19.3.0 core and horizon 2.20.0. One more thing my network was core 12 than I have upgraded it gradually.