From the website:-Changes to services
Until May 2018, services in and out of London Bridge will be affected as follows:
Thameslink Bedford to Brighton cross-London services will not call at London Bridge but will take an alternative route between London Blackfriars and East Croydon
A half-hourly Thameslink service will operate between London Bridge and stations to Brighton off peak on Mondays to Fridays and between 06:30 and 22:00 on Saturdays, with only a very limited service at peak times
Journeys between East Croydon and London Blackfriars are 10 to 12 minutes longer than before, and some services will be altered at other stations

I often use east Croydon and see Thameslink trains stopping there.