Keep plugging iPhones into the same computer and the first thing to fail is usually power at the port, then the hub or the USB controller it sits on, then heat when the phones and power supplies are piled together. The count moves with mirroring, picture quality, cables, and power.
Power runs out first
Each phone has a data cable and is also charging. If the hub only draws power from the computer port, after a few more phones the devices disappear from the list, charging becomes very slow, or a connection comes up and then breaks. Adding CPU does nothing here. Switch to a hub with its own power supply, and plug in the power brick. A data cable alone is not enough.
Cables take part in the power drop too. A cable that is too thin, too long, or making poor contact looks a lot like insufficient power: fine on one phone, and it breaks once it goes into a row of hubs. Swap in an original cable, or a cable of stable quality, and compare. Front ports on a PC case supply less power. Once the device count rises, move to a rear port, or to a hub with its own supply.
Then the hub layer
Power can be enough while the ports still share one USB bus. Ports on the same controller split the bandwidth. Tap commands alone are small and rarely blow up here first. Live mirroring, batch install, and flashing the developer disk image fill that path. A stuck picture, late commands, and failed installs stack on top of each other.
The fix is to split the hubs onto different USB controllers. Keep every port from cascading behind one hub that then cascades into another. Stagger the heavy jobs, disk-image flashing and mirroring. When you need to take more pressure off USB, wireless debugging can move some sessions away, provided the LAN can carry them.
Lights on every hub port can all be on while a path is still unstable. In the control center, see whether a whole row drops together or only the phones on one hub. A whole row means check that hub power and upstream port. Scattered drops mean check those cables.
Heat last
A phone that charges with the screen on, stacked on a rack with no gap, gets hot, throttles, and later shuts off on its own. A hub and a power brick pressed against the back of the phone send heat back into it. If the script leaves no idle time at all, the screen and charging keep working together and the heat arrives sooner.
Heat can show up together with the first two problems. The check still goes in order: confirm every phone is charging and whole rows have stopped dropping, then see whether mirroring has filled a single USB controller, then spread the devices out and lower the mirroring frame rate and picture quality, and see whether the shutdowns stop. When a body is already very hot, stop that phone. Leave the next device unplugged.
The signing quota solves a different problem. An individual developer account is 688 yuan a year, up to 100 registered devices, iOS 12 and later. That is Apple fee. USB HID 10.7.0 (2026-09-08) can skip the board on iOS 17 and later, and it is mutually exclusive with Start Automation. It does not change the current at the port or the cooling.
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