I am not seeing the DHCP errors that you are seeing, but I did look at my Error Logs and the first instance I had of -170001 [TCP-Conn] -256/-140002 Net Module Rule: 14 is:
Mon 2021/11/29 11:04:46 PM System -170001 [TCP-Conn] -256/-140002 Net Module Rule: 14
This is CST, so just after midnight on 12/30 Eastern Time. I assume this is consistent with others? I am trying to determine if it started at the same local time, or all at the same instant globally. I assume the latter, but wanted to check.
But even if that is the case, I am still not sure if this issue is on the IFTTT side since I cannot replicate the issue on any other platform. I have an HTTP app on my Android phone that I can use the same POST configured as close to the settings as I have in my ISY and it work immediately. No errors.