Do you by any chance have a CATC analyzer to observe what is happening on the bus?
For isochronous endpoint since it doesn't have NRDY (or NAK when it comes to USB2.0) the concept of transaction is slightly different than other endpoints. If the host doesn't receive the specified amount of time it'll not have a way of knowing whether it is due to packet corruption of due to lack of response from device. So the host will time out the transaction. Please look at section 8.1 of the USB3.0 spec to understand this better.