Hot restart issues.

The obvious first. A fully charged battery is 12.6-7 v. So if yours measures 12.2 v, it is discharged. Get a new battery. Also check starter cables for good, clean connections.
Hypo pistons expand more because of the alloy content. If they were installed a bit tight, then they will be tighter at operating temp.
If you haven't already got one, I would get a hi-torque starter. Cheapest is probably Road Star, Hornsby, Sydney.