UserWarning: Glyph 26 () missing from current font

I keep getting error:

/opt/anaconda3/lib/python3.8/site-packages/IPython/core/pylabtools.py:151: UserWarning: Glyph 26 () missing from current font.
  fig.canvas.print_figure(bytes_io, **kw)

With the following code:

import pandas as pd
import numpy as np

import matplotlib.pyplot as plt
import matplotlib as mpl

class Raman:
    def __init__(self):
        '''Initialise the class instance'''
    
    def readcsv(self,filename,skipheader=2):
        '''
        Returns the xth column from an input csv file 

        filename : Input csv filename
        '''
        data = pd.read_csv(filename, encoding= 'unicode_escape')
        data2 = data.to_numpy()
        x = data2[:,0]
        y1 = data2[:,1]
        y2 = data2[:,2]
        y3 = data2[:,3]
        av = data2[:,4]
        
        return (x,y1,y2,y3,av)
    
    
    def plotRaman(self, x, y, maxh=300,title='Raman'):
        '''
        Plot Raman spectrum
        '''
        plt.plot(x, y,lw=0.8)
        plt.xlabel("Raman shift")
        plt.ylabel("Intensity")
        plt.title(title)
        plt.show()
        
        
# Introduce class
s = Raman()

#Import csv files 
x_0201, y1_0201, y2_0201, y3_0201, y_0201  = s.readcsv("02_01.csv")
#Plot graph
s.plotRaman(x_0201,y_0201,900,'0201')

My plot output looks like this:

Everything else runs fine other than the plot output.

I've tried resetting Anaconda/ Spyder which I am using and it doesn't work.