Copanlisib and Nivolumab in Treating Patients With Richter's Transformation or Transformed Indolent Non-Hodgkin Lymphoma

Inclusion Criteria: * Diagnosis of Richter syndrome (RS; transformed CLL), or indolent NHL (follicular lymphoma \[FL\], lymphoplasmacytic lymphoma \[LPL\], marginal zone lymphoma \[MZL\]) in transformation. Only patients who have diffuse large B-cell lymphoma (DLBCL) histology are eligible in transformation are eligible (for example, patients with transformation into Hodgkin lymphoma subtype are not eligible). * Participants with RS must have received at least 2 cycles of prior systemic therapy for either RS or underlying CLL. * Participants with FL and other indolent lymphomas in transformation must have underwent \>= 1 prior chemo-immunotherapy regimen (e.g., rituximab/cyclophosphamide/doxorubicin/prednisone/vincristine \[R-CHOP\] or similar) administered for \>= 2 cycles and have had either documented disease progression to the most recent treatment regimen, or refractory disease and must not be candidates for or planning to pursue autologous stem cell transplant, or must have relapsed following autologous stem cell transplant which took place at least 3 months prior to study therapy. * Radiographically measurable lymphadenopathy (\>= 1.5 cm) or measurable extra-nodal disease. * Eastern Cooperative Oncology Group (ECOG) performance status =\< 2. * Total bilirubin =\< 2 x institutional upper limit of normal (ULN). * Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) less than 2.5 x institutional ULN. * Estimated creatinine clearance (CrCL) using the Cockro…