Browsers are being pretty weak to understand difference between local networks vs internet.
Lot of times I have seen hassle caused by HTTPS, be it printer or server baseboard management controller.
It could be one of your public IP addresses—more likely with IPv6, but still possible with IPv4—and not simply "squatting" on someone else's assigned public IP address. The browser may not be aware that these are local.
With that said, the devices should use public domain names and obtain proper certificates for them via the ACME DNS challenge, which avoids the issue altogether.