DPF fitted? Could be blocked.
It wont regen if there is a fault, so you are heading for a big problem, unless you find the fault asap.
You say the hoses are ok, but did you test under boost?
https://www.ebay.co.uk/itm/VOLVO-C30...oAAOSwvcFb973g
Just look at how many of these hoses sell, to replace the rigid plastic OE one.
Its hard to detect a leak