iPhone 12 Pro Max Won't Connect with WiFi-Based App

I'm trying to use iPhone 12 Pro Max with a WiFi-based OBD-II reader in my car. I can make a WiFi connection with the OBD-II device (PLX Kiwi 2 WiFi) but when I open the app (DashCommand) to view info on various engine parameters, the app searches for, but is unable to "find," an OBD-II device.

The DashCommand app works PERFECTLY with my iPhone 6S Plus using the SAME iOS version, the SAME version of DashCommand, and the SAME WiFi settings. Something about the iPhone 12 Pro Max is preventing the DashCommand app from completing the connection with the Kiwi 2, but I cannot determine what it is, or how to fix it. Please help!