If the battery level gets to low the receiver (base unit) will be unstable, potentially causing issues to connect between the App and the receiver. So even if the Blue LED is flashing when sensor is connected and solid when opening the App successfully connection can be a problem if battery power is below a critical level (The App should have notified you if the battery level is below critical level). Try to connect again with new batteries installed. If changing batteries did not solve your problem, then contact us at support@cookperfect.com