Sorry Mate, for two reason.
first, my english is not pretty good, but you find the "invisible" skeleton exactly where is always appeared in this dungeon. I tried to describe this dead end, but visibily not enough well. Finaly you find him so it's cool

he's always at the same place.
You can try to exploit an another bug now if you want (personally i never use it but it's up to you to see if you want or not use this bug) : you can talked again to the priest who give you the quest "evil spirit". Say again to him that you have fullfill his mission (to clear the dungeon) and your relation with the english nation will rise. As soon as you finished at least a faith this mission, you can take advantage at will of the bonuses "diplomatic" of this quest by announcing, again and again, to the priest that the mission is carried out.
And just for Gioco, that's to bad to don't try these quest. At the beginning of the game you can found some very very nice stuff here. It's difficult of course but you can choose where to try it (it's easier of course in some tiny cavern). To have the Cerber sword, or the spanish rapier at the beginning of the game is very useful
and i'm sorry because personally i always found the tablet in the same place : the grotto of dominique. So i don't really know about the village or the inca's place. But, after doing the quest of Sharp, i can say that there are some "deserted" place in the main land to. one of the shore at the north of belize is considered like a deserted place (like cayman, turks etc.) Maybe there's another place in the main who are considered like that. I can't give more information about he tablet, i'm sorry.
But maybe it's impossible to find it with the combined mod. I finish this quest with the standard game. The modification of the items in the combined mod can create a bug with the tablet.... i don't really know, i just ask a question here.