The moody report is only one report and using a single report to determine if a company is worth buying into would be irresponsible with your money. You should look at multiple sources. The Research Team, New Constructs and Market Edge all say avoid due to large debt load, with other equity research saying they are neutral about the stock as of July 20, 2020.
Now the stock is still below it's 6month $120 a share baseline, but other stocks in tech and banking have rebounded much better than Fiserv. It tells you confidence in the company isn't there yet.
My guess, once Fiserv has a solid year under their belt where the debt is reduced without cutting jobs. It will show the company is truly profitable; because, right now the only way they make their numbers look good is cutting expenses. In this case synergies (overlap of employee duties).