as I already explained, the number of FBMC symbols has to be doubled compared to any other waveform, as it uses only real valued symbols. Further, as you employ a subcarrier spacing for cell 2 that is twice as large as cell 1, you again have to double the number of symbols to match the frame duration. Therefore, I suggest the following parameters
scStr.modulation.subcarrierSpacing = [15e3, 30e3]; % select a four times bigger subcarrier spacing in the second cell scStr.modulation.numerOfSubcarriers = [104, 52]; % to have the same bandwidth, the total number of subcarriers must be one fourth on the second cell scStr.modulation.nSymbolsTotal = [15, 60]; % to have the same frame duration, the total number of symbols must be four times higher in the second cell scStr.modulation.nGuardSymbols = [1, 0];
I just tried these settings on the current simulator version and it worked. Let me know if you encounter further problems.