To reproduce, create a resource plan with move trigger, like below:
Now, run two queries in pool1 and pool2 using different users. The query running in pool2 will tried to move to pool1 and it will get killed because pool1 will not have session to handle the query.
Currently, the Workload management move trigger kills the query being moved to a different pool if destination pool does not have enough capacity. We could have a "delayed move" configuration which lets the query run in the source pool as long as possible, if the destination pool is full. It will attempt the move to destination pool only when there is claim upon the source pool. If the destination pool is not full, delayed move behaves as normal move i.e. the move will happen immediately.