There is a known issue in ACME Sales 11.26.1 that can cause unexpected behavior if a customer presents a card to an Ingenico EMV reader before the POS user gets the device into the correct state. Note that if a credit or debit card is given to the card reader while the device still says "Ready" instead of "Please Insert, Tap... etc.". then this can cause the iPad terminal to force close the ACME Sales application.
Workaround: We recommend that when possible, the POS user prevent the customer from submitting a credit card to the card reader until the agent is ready to accept payment. This can include leaving the card reader out of customer reach until the agent is ready to take payment.