Assuming theres nothing mechanically wrong with your CT26, in addition to checking for blockage, have you changed the way the hose is routed? … Have you tried a larger diameter hose, or shorten the length of the hose your now using?
The available suction is a function of the overall suction losses through the hose, and are due to friction losses over the total length of the hose and friction losses which occur at the various connections and bends. These connections can be; hose to tool connections, hose to hose connections or even PVC elbows, etc., that we may introduce into our set ups. Even the bending of the hose, ie., wrapping it around in a spiral configuration etc, can introduce considerable suction losses. The original corrugated hoses are notorious for their increased suction losses. The inside surface of the hose has undulations which cause turbulence in the air stream and increase the suction losses. The new Festool hoses appear to have a smooth inner wall which should reduce the suction loss.
Use the largest diameter hose you have, and the shortest length possible; use the least number of bends and other fittings, and straighten the hose run.