I had a strange experience with nucleoside derivative that had carbon-nirogen bond fission with tetrakis-PPh3-palladium used on a different part of molecule. This reaction was done in methanol with potassium carbonate base. We solved this issue by introducing a more hydrophobic group (TBDMS) into the structure.
Suzuki coupling is well-known to work in plently of solvents, including toluene, THF and DMF, so you can vary that. Also you can try using a different base, like tert-butilates or K3PO4 of even some tertiary amines.