I just disconnected/reconnected the USB to 4-pin JST cable from the microhard carrier board and rebooted the vehicle. Now the wlan0 interface has been up the entire time the vehicle's on, but none of the other devices on the vLAN the wifi adapter is connected to can ping the vehicle over wifi.
Output from dmesg looks the same except the following output after the microhard interface is found:
[ 26.460342] usb 1-1.2: new high-speed USB device number 4 using xhci-hcd [ 26.550901] usb 1-1.2: New USB device found, idVendor=1f94, idProduct=3002, bcdDevice= 4.14 [ 26.550915] usb 1-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3 [ 26.550922] usb 1-1.2: Product: pMDDL2450AES256 [ 26.550929] usb 1-1.2: Manufacturer: Microhard [ 26.550935] usb 1-1.2: SerialNumber: 1592348 [ 26.639101] rndis_host 1-1.2:1.0 usb0: register 'rndis_host' at usb-xhci-hcd.0.auto-1.2, RNDIS device, 16:4f:08:e4:e1:09 [ 26.643401] cdc_acm 1-1.2:1.2: ttyACM0: USB ACM device [ 33.765387] vdd_tof: disabling [ 33.765393] vdd_hap_boost: disabling [ 37.240138] hrtimer: interrupt took 112083 ns [ 101.412343] boot log copy done [ 114.937520] qcom_rpmh DRV:apps_rsc TCS Busy, retrying RPMH message send: addr=0x41b08 [ 233.747906] perf: interrupt took too long (2778 > 2500), lowering kernel.perf_event_max_sample_rate to 72000 [ 339.990578] perf: interrupt took too long (3473 > 3472), lowering kernel.perf_event_max_sample_rate to 57500 [ 386.060248] perf: interrupt took too long (4425 > 4341), lowering kernel.perf_event_max_sample_rate to 45000