You are using Migration Cockpit used to load Bank account balances, the balance is reflected in the cash flow analyzer report, but not in the GL balance reports.
SAP S/4HANA Cloud
Reproducing the Issue
Use Migration Cockpit used to load Bank account balances, then check the GL balance reports, for example app Display G/L Account Balances.
Bank account balance upload will only impact cash management reports and apps.
If you load G/L account balance in a way that there is an accounting document posted, cash management can integrate such accounting document and generate relevant information in cash flow analyzer report, therefore the same balance can be shown in cash report, it is not necessary to upload bank account balance again; if G/L account balance has no accounting document posted but is just for reporting purpose only, cash management will not be updated, in this case you will need bank account balance upload for cash management purpose.
This is standard behavior.
Migration Cockpit, Bank account balance, cash flow analyzer, G/L Account, G/L balance report. , KBA , FIN-FSCM-CLM , SAP Cash Management , How To