You can, however, fix these things yourself without having to delete or redo anything. First, open your config.yml file and remove the value random. The correct value is random_arena which should stay. Next, open your arena.yml file. For each arena that you set a reward for, do the following:
Add a new line after reward:. This line should be at the same layer as the cmd: ... line. Copy and paste: active: cmd
This should make your reward work again, if not, try to re-add it though the new command.