Is is it doing the same thing or different? Meaning do sticks just reboot from lower to higher frequency or they drop out completely? What's the CPU usage?
Mine is at 20% now, running 16 sticks at 500Mhz

The way to see that your USB bus is overloaded is your CPU usage, it will skyrocket. It only happened when I plugged in another hub WHILE cgminer RUNNING. When it happens, just stop cgminer (ctrl-c) and run it again, to save your PI from extra heat, it should zoom at around 20% normally.
If I plug in and turn all hubs on BEFORE i run it, it would just find x amount of sticks (not all) and just run normally at low CPU load.
So, it the cgminer that gets confused by all the hub stuff and goes nuts.

Btw, I'm only using USB 2.0 ports (white inside), don't use USB 3.0 ports (blue inside)
Try only running 2 USB wires to PI (to USB 2.0 ports!), only from 2 hubs, rest of the hubs just interconnect, meaning connect the wire from hub 1 and 2 to PI, as for the other hub - just plug in the USB wire to hub 1 or 2. Let me know if it works. You can plug in keyboard/mouse directly into your other 2 ports on PI.

Check this out - https://forums.raspberrypi.com/viewtopic.php?f=28&t=53832

I finally figured it out. I'm running 16 sticks now @500Mhz on 2 hubs. Probably can even run on single hub, but will need voltmeter and pod adjusting...

My problem was that both of my 30 port hubs are constructed with 8 usb hub chips each. Each chip controls 4 ports, so its like 8 separate 4 port hubs connected.
For my two hubs system actually sees 16(!) 4 port hubs. It just cant support that many hubs.

Each hub has 2 usb cables, one for each side, so each usb cable supports 15 ports or half the hub. I originally had all 4 cables plugged in into the PI.

What I did - I only connected 2 cables to the pi, each cable goes to a half of each hub and loaded them with sticks (with single port spacing)
This achieved voltage/amperage needed to run the sticks (both sides share the power line) without overloading the system with amount of hubs connected.
I can only run 16 sticks this way, it will do for now.

Hope this makes sense.

Are you running multiple hubs?
If I use them on single hub, I can usually run up to full hub, which is 15 on mine and won't be surprised it would run all 30 for few mins until voltage will get too low and they will start rebooting (30 port industrial hub with some spacing in between, every other port)
In order to stably run more then 9 I would need to dial in the pod on each, voltage gets too low on my hub...
My PI4 CPU actually stays around 20%, But if I plug in the second hub and/or start splitting sticks in between, THEN it goes nuts, like 80-100% and sticks start to zombie out, the ones that been hashing for a while, new ones don't appear,
Interesting enough - all sticks are flashing the white diodes (like they are hashing), even the ones that system does not see...

The problem is multiple hubs.....