After practicing the spiccato stroke on its own, add in the variable of string crossing.
As the string crossing action here is mainly whole arm, watching your bowing action in a mirror or video allows you to check that the spiccato action is coming from the forearm or the hand leaving the upper arm to travel with the whole arm for the string cross.
The string crossing action needs to be fluid enough to allow the bow to contact each string with a ringing sound.
Practicing such patterns can be a brain teaser and it may help to write out the pattern of the open strings.