Kv6 new thermostat leaks?

[Shuriken_57]

Good morning, gentlemen.
When I fixed my fuel leak, I also replaced my thermostat because it was cracked and leaking.
I did install the new thermostat from dmgrs.
I followed rave procedure for coolant purge.

Yesterday morning , I saw a spot of coolant on the ground.
I checked the engine compartment and to my surprise, there was coolant under the thermostat.
I wondered if I had incorrectly refit the new thermostat . So , I started the operation again.
When I finished the job, I drove with the vehicle, the thermostat works well. I checked the thermostat on the way home and there were no leaks.

Today, I didn't use the vehicle, I inspected the engine compartment this morning and no trace of coolant.
But tonight, I wanted to take the vehicle out and there was coolant on the ground and under the thermostat.
How could the thermostat leak when I did not use the vehicle? This morning everything was clean, I don't understand .
Do you have an idea?
Thank you. ( I specify that I used the keyhole method)