As you correctly mentioned, there are key risks that can be associated to all the phases of M&A transactions. To name a few, starting from due diligence, not having considered all the financial aspects of the target, or not having conducted a proper research and investigation, can have the risk for the buyer to buy at a higher price and have impact on the value of seller; not having considered how to properly manage the integration, then, can be disruptive and can either delay the proposed timeline (sometimes never reaching its original and planned goal) or having massive consequences, such as poor retention from the acquired business. These two are the areas in which I have a bit more knowledge about, and other experts can give you more detailed analysis or provide further examples.