The purpose of this study is to investigate nivolumab combined with Debio 1143. The study will focus on subjects with specific solid tumors for whom tumors were previously treated with anti-PD-1/PD-L1 therapy as a single therapy (or when used with other cancer therapies), but the tumors have worsened despite treatment. The study will also focus on subjects whose tumors have initially responded but have stopped responding to treatment. This is a Phase Ib/II study, which means that this study medication will be tested for the first time as a combination treatment in humans. This study is divided into two main parts, Part A and Part B. You will participate in Part B of the study. Part A of the study must be completed first before Part B can begin. The main purpose of Part A is to find the optimal and safest dose of Debio 1143 to use when taken with standard doses of nivolumab. The results from Part A will determine the dose of study medication which will be used in Part B. The main purpose of Part B, in which you will participate, is to see whether the new combination treatment works in subjects with different types of cancer. Part B of the study will also look at how safe the study medication is and evaluate any side effects. Between 32 and 60 subjects will participate in Part B of the study. The study will also look at other things, including • What your body does to the study medication (“pharmacokinetics,” or PK) • How the study medication affects your body (“pharmacodynamics,” or PD) • Levels of antibodies that the body may produce against the study medication (called anti-drug antibodies, or ADAs) • How your genetics may influence how the study medication works in your body (“pharmacogenetics,” or PGx) and how you are responding to the study medication by looking at biomarkers (substances in the blood or tumor). This type of research is done by examining samples of your blood and stored tumor tissue. The PGx part of the study is optional. If you decide that you want to participate in the optional PGx part, you will need to read and sign a separate PGx ICF that the study doctor will discuss with you.