Ok it's definitely working now.
At first after I tried your listed steps by clearing the cache and resetting the game it appeared to be fixed but after I restarted the game the issue cropped up again.
I had to reset the cache/game twice and now it is working and has been through several game restarts.
Thanks for the help!
I have roughly 30k free experience that I would like to convert and I have more than enough gold to do so.
I make sure the locker is unlocked
Click free Exp
Ensure all tanks are selected
Click Convert
Game shows Aslains loading content and icon for about 30 seconds
Screen then goes black for about 15-20 seconds
Screen then shows a blank page
Screen then returns back to the convert menu with nothing converted
Aslains_WoT_Logs.zip