Blitz Dual Turbo Timer

My first post on the group for perhaps 5 years!

I fitted the above timer about 8 years ago. Purchased from new, it worked flawlessly. I think it has the official wiring harness adapter fitted. It runs the mod that allows the factory immobiliser to work in conjunction with the timer. On a pre-MOT check, after having not driven the car for about 3 or 4 months, I started her up. I noticed that I could hear the turbo timer beeping as if it was counting down. The keys were still in the ignition in the On position, and it was still running. After a short time, the engine stopped running.
I checked the battery voltage - seemed healthy.
Unplugged and re-inserted the plugs to the turbo timer display unit and its black box under the dash. Still the same.
As the MOT was the next day, I just decided to disconnect it. So I unplugged the display unit. Still the same result.
Then I unplugged the black box as well. The ignition then behaved normally.

Bit of a rambling post.

Any ideas what I should check?

Open the unit up and check for leaking capacitors?

Thanks for the reply.
So does it sound to you like it’s a failure in the black box?

I recently had the exact same thing happen. I put it down to a flat battery been fine since