Spindle start up and the cuts out

I have a 1.5 kw PWN water cooled spindle. My control board is a Sienci labs slbext. When I press start the machine goes in motion. The spindle starts and the seconds later shuts down. I am able to subsequently run the spindle manually. Hopefully you can give me some guidance. It doesn’t happen all the time but I’d love it if it doesn’t occurred

My email is cfid5@aol.com. My cell # is 203-509-435

Thank you in advance