I wish I had read this thread before replacing DPF. First, I replaced G450 sensor but didn't adapt it to ECU via VCDS.
The new sensor did nothing actually without adaptation as many people complained. I ended up replacing DPF (not sure if I really needed to replace DPF or not, though).
The DPF problem continued, but after adapting a new G450 sensor (thanks to this thread), the DPF regen started when DPF blockage reached 40% and cleared DPF completely to 0% - first time since DPF/G450 failed.
Now, % doesn't go up so quickly anymore. I will post the whole story replacing DPF and G450 sensor later. My problem was caused by the engine oil overfilled, I think.