It has been reported in several papers that if you use Pt as a counter electrode, then Pt undergoes corrosion and metal Pt is formed on the working electrode. Pt on working electrode works as a catalyst for water reduction. You cant try to use a graphite as a counter electrode.

I would like to add that sometimes it happends when the set up is not correct or the cables do not have good connection.. If you have increased noise, check again the counter electrode and reference electrode.. Check as well if there are bubbles in the glassy pump of reference electrode.

I agree with Yurii V Geletii , also sometimes electrolyte could leak to contact and make a real mess.

I would like to add: try to do the electrochemical cleaning of your tip as sometimes only mechanical polishing is not enough to bring back the tip into its original state

In addition to the above comments. Make sure that you removed completely oxygen from the solution, and check may be some impurities appeared in the solution or in the membrane of Ag/AgCl. The point is also that at high anodic potentials molecular chlorine, HCl and HOCl appear in the solution.