1- Increase purging pressure
2- If u replace bags after 3 years, now do it after 1.4 years.
3- check ur pressure control diaphragms and pressure regulator diapghrams, if any of them is damage replace it.
4- check leackage in air tube for controller.
5- check leackage in purging pipe joints and their damage or loseness
6- check that the high pressure pipe before and after pressure regulator is not less then 1.25 inches diameter.
7- make sure ur pressure regulator is working properly
8- use the bags of more permiability then before as now partical size reduced and they stuck in pours of BF.
Last thing, if ur mill is stopped and suction fan is also stopped than purging must continue all the time.
Hope u find your solution.
Contact info: engr.abdullahahmed@gmail.com