Sharp sample transition in OFDM signal
You're running a DAC at 5 MS/s and have a reconstruction filter of 50 MHz bandwidth.

There's your error: You're not doing proper reconstruction filtering! Reduce the filter bandwidth to reflect your sample rate.

You can of course also interpolate your signal 10× and set your DAC clock to 50 MS/s. Interpolating an OFDM signal is potentially very easy: Just add enough unused carriers to the side (note: you might need to adjust your CP length and synchronization algorithms).