Hello,
What type of eye diagram are you expecting for the Gaussian Mono Cycle? Fundamentally, the modulation schemes are different between a NRZ pulse and the monocycle gaussian format. From the eye diagram it looks exactly as I would expect it to considering the modulation type and the input electrical signal.
Our BER Analyzer assumes an NRZ or RZ modulation format and calculates the BER from the eye diagram based on that, which of course does not apply to this application. In your case the best bet is to use the BER Visualizer for a quick visualization of the signal, but I think for a rigorous BER calculation you will need to use the BER Test Set. There are plenty of topics on the forum on the use of the BER Test Set if you are unfamiliar with it.
Regards