Custom event and action not triggering in UAT environment when i was trying to do it manually or automatically but remaining environments its working good ,workflow used in custom action could anyone please tell me the solution for this ?

in serial object screen two fields should be triggered and updated. one field(a column) is only when new value added in some other table (1table). another filed(b column) should be updated when the data newly added or modified from that respective table(2 table) but its not happening .