All C&P cards are subject to various limitations and requirements as far as transaction authorisation is concerned. This is built into the Chip so that your card determines whether it needs authorisation to complete the transaction. The banks will not tell you how your card is set up, else you could work out how to circumvent the requirements. Hence, when you ask, you are simply told that there is nothing wrong with the card - there isn't, it's doing exactly what it's supposed to do!
All that the entry of the PIN does is to confirm that it is the proper cardholder making the purchase.
On-line authorisation is required in various situations, no matter how good your record with the card company. At worst, for a customer with a bad record, on-line authorisation will be required for all transactions. Even a good customer will be put through the authorisation process in certain circumstances.
Avantix Mobile does not handle on-line authorisation so as soon as a card asks for authorisation it aborts the transaction. Other ticket machines are dependent on the comms links to the card authoriser working correctly. Any failure of the TOC's wide or local area networks could mean that this isn't the case. Similarly, high levels of usage could create a bottleneck in the process which causes transactions to time out.