Island Levels on Skyblock

I was just wondering how island levels worked on Skyblock. When I first properly started building on my island it was a negative value, which I asked about about and others didn't really understand themselves. Because of this, while I was building I checked my island level often and realised that the level was going up very slowly and then I left my island for maybe 2 minutes and when I can back it seemed to have dropped back down to level 0. Could a developer or a senior member of staff look into this or if there is no problem, please explain to me how it's supposed to work, Thanks:)