Bank reconciliations (described in https://help.propertymatrix.com/en/articles/1119072-bank-reconciliations) will link all the transactions in the reconciliation form to the created reconciliation transaction. These transactions cannot be deleted since they make up a part of that reconciliation's balance calculation. This applies both to transactions that are cleared and transactions that are not cleared.
Transactions that are cleared are part of the bank balance at the time of the reconciliation, so deleting them would cause the bank balance to change and the reconciliation would no longer balance.
Transactions that are not cleared are part of the difference between the Property Matrix bank account balance and the real world bank statement balance. Deleting these transactions would cause the adjusted balances to not match. This is a simple example of why deleting these transactions would throw off the reconciliation's calculations:
The Property Matrix bank account balance and real world bank statement balance both start off at $100,000.
A check is written and printed from Property Matrix to pay a vendor $5,000 for work done. The Property Matrix bank balance is now $95,000.
The vendor does not cash the check this month.
At the end of the month, a bank reconciliation is done in Property Matrix. The Property Matrix bank balance is $95,000 while the real world bank statement balance is $100,000, so the amounts do not match.
The bill payment for $5,000 is left as unreconciled. This then shows up under the calculation section for "Outstanding outgoing transactions", and adds the $5,000 back to the Property Matrix bank balance as an adjustment for the purpose of reconciling the account. The adjusted Property Matrix balance is now $100,000, which matches the real world bank statement balance. Submitting the reconciliation will link that bill payment transaction to the newly created reconciliation transaction.
Deleting the bill payment transaction would then cause the reconciliation calculation to not balance since there are no more outstanding outgoing transactions, and the Property Matrix bank balance is $95,000.
If you need to reissue a check or void a transaction that is part of a past reconciliation for any reason, you should use the 3-dot menu option for "void" or "refund" on the transaction you want to void. This will create an offsetting transaction which will then zero out the original transaction, and both can be marked as cleared on the next reconciliation.
If you really need to edit the transaction directly for any reason, you will need to delete the linked reconciliation first. Then you can edit the transaction. The reconciliation will then need to be recreated since the previous reconciliation balances no longer balance.