Recordings getting shorter than programmed

Hi. I hope all is well. I bench tested a couple of Audiomoth units connected to a power bank. I set up the recording schedule (attached) and everything was recording well. After around two days of almost continued recording with the programmed schedule. A pattern emerged every few recordings were shorter and then back to what was programmed. Please advise on these issue as it happened with several units and how to prevent it. Thank you