Rendering imperfect HTML

I recently received an important message from a credit card company that in eM Client displays as a completely empty message body. We have two other email clients available: Aquamail for Android, and Apple Mail, and in both of these the message appears and seems to be normal and complete.
I’m not an HTML expert but I’m fairly sure that the message code is faulty. It’s hard to check because the “view message source” function introduces extra characters for word wrap, and the code is the usual vastly over-complex mess. But I think very likely it’s an error that has the effect of a missing end comment (–>) so that the part that should be visible is commented out.
So eM Client might be correct in rendering it blank - but I presume most people who receive this message can see it so is eM Client the only one in step? In this case it was obvious that something was wrong but in another message it might be possible to miss only a paragraph and we might miss something important. It’s a bit worrying. Is there a big difference between the rendering engine in eM Client and those used by other clients?