You thinking it may be a physical interference? How would it clear itself without causing either lots of smoke or damage?
Ok this is totally theoretical.lol I’m may be completely wrong, I’m just thinking outside the box.
Let’s say for this scenario fuel has filled a cylinder. When you attempt to start it, the high torque starter puts a good amount of pressure on the assumed hydro locked cylinder.
With the pressure from the attempted start, a small amount of assumed fuel slowly seeps by the rings. After a few attempted starts, either valve starts to open, the hydrolock would be released. Now the engine can freely turn over.
So let’s now theorize that it’s a head gasket leaking coolant into a cylinder.
In this scenario, maybe the coolant only leaks into the cylinder very slowly, after the engine has been up to operating temperature, and there is pressure in the cooling system.
Now after the attempted start, the coolant is slowly being pushed back into the cooling system the same way it entered. After a few attempts to start the engine, enough coolant has been pushed back out of the cylinder that either valve opens. The hydrolock would be released.
Again, I‘m throwing pasta at the wall and seeing if it sticks..lol
An easy test would be, the next time it won’t turn over using the starter, just put a breaker bar on the crank pulley/harmonic balancer bolt, and see if you can turn the engine over by hand. Just remember to try to turn it in the right direction.
One full rotation would answer the question. Now if it’s not turning by hand, pull out the plugs and crank her over with the starter. You will see gas or coolant shooting out of a cylinder.