tresspassing is typically initiated by the host, incorrect failover mode, host connectivity issues ? If these are pool LUNs you want to make sure they are always on the same SP they were allocated from. If you look at LUN properties it will say "Allocation Owner".  If i have a couple of trespassed LUNs, i typically trespass them back late at night.
i have a vnx5300. why would random luns tresspass from one sp to another?  what is best practice around tresspassing them back?  
lun tresspass