I'm a new user to Mint as well and experienced a similar issue. What i've realized is that my 1st budget was created towards the end of March 2016 and when April rolled by, I lost all my budget. I tested this by creating a brand new budget during the beginning of April, made some minor adjustments during the month of April; now that we are in May, my budget looks fine.
Other users reported similar behavior on this post and apparently this is done by design from the developpers:
People come to Mint for help and answers—we want to let them know that we're here to listen and share our knowledge. We do that with the style and format of our responses. Here are five guidelines:
Keep it conversational. When answering questions, write like you speak. Imagine you're explaining something to a trusted friend, using simple, everyday language. Avoid jargon and technical terms when possible. When no other word will do, explain technical terms in plain English.
Be clear and state the answer right up front. Ask yourself what specific information the person really needs and then provide it. Stick to the topic and avoid unnecessary details. Break information down into a numbered or bulleted list and highlight the most important details in bold.
Be concise. Aim for no more than two short sentences in a paragraph, and try to keep paragraphs to two lines. A wall of text can look intimidating and many won't read it, so break it up. It's okay to link to other resources for more details, but avoid giving answers that contain little more than a link.
Be a good listener. When people post very general questions, take a second to try to understand what they're really looking for. Then, provide a response that guides them to the best possible outcome.
Be encouraging and positive. Look for ways to eliminate uncertainty by anticipating people's concerns. Make it apparent that we really like helping them achieve positive outcomes.