I didn’t have any problem connecting to iPhone hotspot with mt300-v2 (on3.025) … but I gave the router away in January so if there has been a significant update then that could have caused issues.

I did notice that the iPhone was a bit finicky for wired tethering if WiFi and Bluetooth were activated though. I found that there was particular issues with USB tethering when the iPhone had the v2 router as a saved WiFi network.

Perhaps you could try deleting the v2’s WiFi network from your iPhone before trying WiFi tethering?

In any case, it’s not the answer you’re looking for but maybe provides some clues.

BTW USB tethering was pretty reliable for me once I ironed out the kinks but the throughout was lower than with WiFi tethering. I found USB tethering much better for extended use overall (on the iphone regarding heat and battery)