Joanne Davenport, good evening again.
What could be happening is that during a Service, a lot of moisture is released whilst singing and a lot of people talking Etc. after the service.
The above will lead to a massive spike in water vapour in the air, not that you can see it, but it is a perfectly natural part of the make up of the air we all breath, but in this case there will probably be a lot more water vapour this is called Relative Humidity.
As an aside, we all breath out water vapour that is normal, when singing a lot more water vapour is created + the heat makes most perspire as well.
Given that your building is very, very warm, the warm air is more than capable of keeping this vast quantity of water vapour / moisture that cannot be seen in suspension. When the building cools down at night the temperature will fall, the water vapour cannot be held in suspension so it MUST appear somewhere as a form of Condensation,
Given you do not have windows which could be opened to vent the warm moist air the room will hold lots of built up water vapour.
if your floors are [say] Concrete or stone slab under the Lino then that floor will be the largest coolest area of the room and that is where where the water vapour will condense into water droplets.
One possible test of the above?? if you or someone in the congregation has or has access to a "De-Humidifier" switch it on as you leave the building at night, would be of interest to know the results you get by the next morning? is the De-humidifier full of water??
Hope this may assist?
Ken.