Highest Dose of Uproleselan in Combination With Fludarabine and Cytarabine for Patients With Acute Myeloid Leukemia, Myelodysplastic Syndrome, or Mixed Phenotype Acute Leukemia Relapsed or Refractory That Expresses E-selectin Ligand on the Cell Membrane

Inclusion Criteria: * Patient must be enrolled on APAL2020SC (NCT04726241)-Pediatric Acute Leukemia (PedAL) Screening Trial - Developing New Therapies for Relapsed Leukemias - A Leukemia \& Lymphoma Society and COG Groupwide Screening Protocol * Patients must be \>= 1 year and \<18 years of age at the time of study enrollment * Patients, with or without Down syndrome (DS), and with de novo acute myeloid leukemia, therapy-related acute myeloid leukemia, myelodysplastic syndrome with increased blasts (MDS-IB), therapy-related myelodysplastic syndrome with increased blasts (MDS-IB) or mixed phenotype acute leukemia that expresses E-selectin ligand on the cell membrane according to APAL2020SC screening results and meet one of the following: * Second or greater relapse or refractory AML as defined below, including isolated extramedullary disease (EMD), but excluding isolated central nervous system (CNS) or isolated testicular disease. * Second or greater relapse or refractory myelodysplastic syndrome (MDS) with increased blasts (MDS-IB). * Second or greater relapse or refractory mixed phenotype acute leukemia (MPAL) * Note: Documentation of E-selectin expression by multidimensional flow cytometry (MDF) at the central laboratory (Hematologics, Inc.) on the most recent bone marrow sample prior to the diagnosis of the current relapsed or refractory disease is acceptable for eligibility to this study in the event of isolated extramedullary disease, inability to obtain a b…