Could be something to do with the multiple-DMA-devices bug discovered in Buster 11. (Were you aware of this?) I think A3000 SCSI counts as a conflicting device. What else is in the A4000?
A software conflict is also possible. Try narrowing things down. Boot without a startup-sequence and load Workbench manually after running/not running SetPatch. And what's in your WBStartup?