Clear. So we will need logs when this behaviour is reproduced. Please submit from both sides, not forgetting the client sides logs as well. Please see the instructions here for those: https://kb.nomachine.com/DT09T00266. For clients side logs please refer to the section “Fourth Step: Collect Client Side Logs”. You can submit them to forum[at]nomachine[dot]com.
If the smartcard has a UBS interface, could you try forwarding the device using the USB option instead? Does it show?
https://kb.nomachine.com/DT09T00266#4.3.
Edit: Submit a new topic if the issue re-occurs.