[Nighthawk M1] B40 2300MHz and B7 2600MHz signal cannot be improved by external antenna

New test is coming. Let's say two antenna connectors are A and B, and two external antenna ports in M1 are a and b.
I tried, A-a only, A-b only, B-a only, B-b only, A-a/B-b and A-b/B-a, all same results.

But found an interesting result, at the first 30 seconds when plugging one external antenna into the left external antenna port, the 2300 MHz and 2600 MHz signal strength did increased from -125 dBm to around -90 dBm, but it shows 3G parameters, the firmware or system seems treating those 2300 MHz and 2600 MHz signal as 3G signal. It's kind of strange.

Please have a look at the screenshot: https://photos.app.goo.gl/4iCCvw33FwEAKbJr6