The £30/£60 is an authorisation hold as explained here. We need to wait for the charge point operator to send us the correct amount for the session. This usually happens very quickly. However, it can sometimes take a little longer while their systems run checks to ensure no payment is due, particularly for unsuccessful charges.
For sessions which failed to start, we release your authorisation hold after 24 hours. Your bank can take a few days to reflect the correct amount, at which point you will no longer see the £30/£60 on your bank statement.