1st gen contact sensor

Hi everyone. I'm just looking for a small piece of your wisdom :) I have a 1st gen contact sensor and no matter what I do, I cant seem to get it to work. I have several of them in the house (I've had them for around a year) and they're all fine apart from this specific one. It stopped talking to the app, and I assume the alarm base unit. I've replaced the battery with a new one. I've done the thing with the battery and the tamper button at the same time, but all I get is one flash of a blue light and nothing else. I've tried adding it back in to the Ring app by capturing the QR code, and the app says it may take a few minutes for the device to be added, but 3 hours later I'm still waiting. Is there anything else I can do, other than bin it and buy another one? I've searched the forum but didn't find anything to help. Thanks a lot! Allan