Hi, Nordic! I have used NRF52840 and SDK 13.0.0. From Errata:
3.18  USBD: EPDATA event is not always generated
Use the USB stack provided in Nordic's SDK.
We have used USB stack from latest SDK. But event "Tx success" is missed sometimes. In host side the last packet present.
What can You tell about this problem? Is this will be present in serial chips?
Update: In attachment a modified example from SDK.
Open serial port in terminal.
Push button 1 for begin tx transfer.
Send some data from host to device.(I have pressed any key in Putty by minute)
When tx transers stopped press again button 1 and look in log.(TxSuccess = TxRequested - 1; in host we can see all TxRequested transfers)
Update 2: Rx transfer event can also missed.