I have a bug with my account 3100. all the transactions in 3110 and 3120 shows in the account 3100 aswell.

Hello @ja_bookkeeping ,

That would only happen because 3100 is the parent or top-level account, and 3110 and 3120 are sub-accounts of 3100.  Anything that gets posted to the sub-accounts show up in 3100 as well, but the original transactions would be in 3110 and 3120.  If this is unintended, then you would remove the sub-accounts from the parent account by going into the account set-up and removing the checkmark from Is sub-account.  This will solve your problem if this setup is unintentional.

But there are many reasons why people might want a top-level account and sub-accounts underneath it because they are related, and they want all entries from the sub-accounts to roll up into the top-level account to see the total for that 'section' of accounts.  So it's possible the accounts may have been set up this way by design.