The problem here is a number of your filters are not set with the correct bandwidth. I set the WDM Demux/Mux to Rectangular filters and 50 GHz bandwidth. The problem was the two signals were too close and the Gaussian filter was not completely getting rid of the other signal.
I got the OFDM part to 0 BER. I’m not sure how the transceiver is working for the UWB part, have you looked at the time domain output after that signal multiplication? There is no electrical signal.