pool name: [spot] - what is it? where is it coming from?

Can you share the screenshot and output of following

select * from resource_pools
select * from resource_queues

Sorry, I can't post that information.

But no, the pool name "< spot >" does not exist in resource_pools.

And as mentioned in the question, I found it in the table resource_queues table.

It's not a resource pool exactly, but rather indicates the query is in queue and not in the resource pool yet.
Between the time a query arrives at the resource manager and when the node schedules a thread to marshal it through the resource manager, the query will be on something called the "spot queue" and thus will appear this way on resource_queues.
If queries remain on the spot queue for any length of time, then there is something iffy going on - most likely due to a sub-optimal resource pool design.