Guide
Picking a USB hub
The hub is the part people cheap out on, and it is the part that produces the most confusing failures.
Why unpowered hubs fail
A Mac's USB port supplies a limited amount of power, and an unpowered hub splits it across everything plugged in. One phone is fine. Four phones charging while their screens are on will exceed it, and the hub browns out.
What you see is not a clean error. Phones disappear from the dashboard and come back, sometimes mid-run. That looks like flaky software and is almost always power.
The symptom to recognise
If devices drop off only when several are busy at once, and everything is stable when one runs alone, the hub is the cause. No amount of software configuration fixes it.
What to buy
- Powered, with its own adapter. This is the requirement everything else depends on. A hub with no barrel jack is not a candidate.
- Enough headroom per port. Budget around 7.5W for each iPhone. A 60W supply across eight ports is comfortable; 30W is not.
- Data, not charging-only. Charging hubs are common and cheaper, and they do not carry data at all.
- USB 2.0 is sufficient. The automation protocol is light. Paying for 3.2 buys nothing here.
Cables matter as much as the hub
Cheap cables are the second cause of the same symptom. Many are charge-only, and many more lose data at length. Keep the cables that shipped with the phones, or buy MFi certified ones, and stay under a metre.
Past four phones
Rather than one large hub, use several smaller powered ones on separate Mac ports. It spreads both the power draw and the bus contention, and when something does fail it takes out three phones instead of twelve.
Past roughly ten phones on one machine, the constraint stops being USB and becomes the Mac itself: each active device runs its own harness process.