Check dmesg for messages about the device not being enumerated due to
excessive current usage or something, if the hub is not externally
powered. The USB OTG port will only enumerate devices with a declared
current usage of equal or less than 100 mA.
I have my 4-port hub plugged into the USB OTG port. There are no messages that appear in dmesg when I connect or remove my pl2303 (sewell brand) usb->serial converter device via the hub. Neither is there any messages when I connect or remove the device directly to the USB-OTG port.
There are also no messages that show up in dmesg when I disconnect the hub ...
(Another tidbit, when I do connect the USB-OTG port to my desktop PC, the desktop PC notices something was connected, but cannot identify it.)