Unwanted peaks in the output of a Notch filter

Hello, I recently tried to implement an IIR Notch filer that will help me remove the 50 Hz noise in the ECG signal we acquired in the lab. The 50 Hz is getting attenuated but then an unwanted peaking is observed at 48Hz while taking the fft. Is there any way to get the desired 50Hz suppression with minimal peaking of such kind? This is my code:

d1 = designfilt('bandstopiir','FilterOrder',8, ...
               'HalfPowerFrequency1',49,'HalfPowerFrequency2',51, ...
               'DesignMethod','butter','SampleRate',Fs);
 buttLoop1 = filtfilt(d1,X1);