Bosch Serie 8 WTW87560GB extended drying time

My bosch condenser dryer has suddenly started to have significantly longer drying times (5-6 hours versus 1.5 hours) and even afte this time clothes still feel damp. The dryer is generating heat, when I open the door it is very humid in the chamber, and moisture and fluff can be seen around the vent as if the moist air is not being drawn away successfully. Some water is making it to the collection drawer but not as much as I would usually find. All the filters are clean and are cleaned after every use. Any suggestions what the problem could be? Thanks.