Lost experience points

That's when I lost,one after I completed that building

I think it has something to do with the 'auto save' of the game, sometimes it will happen to me ill tap all my buildings and collect the money, then next time I go on it will be the same as the first as if I have t been on

YES!!!! I built El Chemistri and went from 60k XP to 13k and now, I am down to 7k. This is probably one if the glitchiest games I have played in my life. Why can't EA get it together? It's a good game and great franchise...don't F this up jerks!!!

My friend has a similar problem, his XP won't go up.

How many xp did you have before you finished your building?

I'm asking because I have noticed that when I finish a task set by the game (build this or that house, make X do this etc.) and collect the xp, I get twice the amount I should have. When I exit the game or visit neighbours and enter the game again, half the points I received in the first place would have gone (and rightfully so, since I got twice as many as I should have).

And I could not help but notice that you actually missed 21000 xp.