scroll id is too long... sounds to me that the number of shards are huge too? how many shards that you have?
I have 2,042 shards and 78 index, around 166.9GB is the size of my data
jepp, longer shards will produce long scroll id...iirc, the scroll id actually contain some information where the scroll position in the shards. either you reduce the shard count or you find a way to store the scroll id somewhere, perhaps in your application server.