I want to make sure I understand you correctly, so forgive me for being so verbose:
You purchased 5 Cores. Of the 5, you were able to setup and configure 2 of them without issue. Of the remaining 3 that cannot currently connect, one of them was configured correctly at one point, because you were able to update it through the web IDE. But, it didn’t successfully update, and now, even after a factory reset, it cannot connect to Wi-Fi?
Can you give me some more information about the other Cores? Did the SmartConfig process work, or are you configuring them all using PuTTY? What does the status LED display–it’s the most useful tool for helping us debug connectivity issues? Could you provide a video that might give me some more information about the status of the LED?
Also, if you haven’t already, you should refer to our troubleshooting guide, which is current with all of the best fixes for known connectivity problems. I hope that helps. If you provide some additional information, I’m happy to troubleshoot further. You can also email us at firstname.lastname@example.org for additional support.