Today, after I changed the relational database that feeds the cube from compatibility level 100 (2008) to 120 (2014), the cubes no longer process (we had to stop the process after taking 5+ hours instead of the usual 10 minutes). The problem is indeed CL change since after reverting back to 100, it fixes the issue.
I have not seen any documentation regarding this issue or I cannot even understand what is the issue, because SSAS was NOT changed at all... the only change was on the DB for the DB-engine side.
Please note again that I changed the CL , not on the cube/SSAS, but on the database that has the fact and dimensions. Any help is appreciated. Thank you very much in advance.