This effect can occur if sufficient stored energy remains within the data-logger allowing it's CPU to remain 'alive' and in a 'sleep state'. The data-logger's CPU will enter a sleep state as energy available to it depletes. After removing the data-loggers batteries, its possible for stored energy within the data-logger to power the processor in a sleep state for up to 10 minutes. Consequently its possible that the CPU can remain in a sleep state even after new batteries have been installed!
To resolve this effect, the data-logger's CPU needs to be reset. Do this simply by removing the batteries from the battery compartment and allow the data-logger to rest for 10 minutes. Re-install the batteries. The CPU will reset, power up and behave normally.