Legend colours are getting same colours

I am using Route & Flow map (Custom viz) to show some routes (Train, Sea, Aero plane, Truck). I have given different colour for each legend. It works perfectly when we open it for first time (as seen in pic 1) but when go to page 2 & come back to page 1; the legends got same colour (default) as in pic 2.

I tried clearing cache & using latest version (Version: 2.75.5649.861 64-bit (November, 2019)