Bottom of prints being cut off

[titaniumapple 4]

Hi, every print I make with my Ultimaker 3, it seems to slice off the bottom of the print (about 1-3mm I estimate). For example, a cylinder on its side will have a flat base when it should be curved!!

Why's it doing this and how can I stop it? I'm using the default settings for UM Nylon and UM PVA.

Thanks!

[Travis7s 22]

I had this happen and the problem was I changed a printcore and manually leveled the bed considerably. Then I forgot and went back to the original print core. Didn't realize but the nozzle just pressed the glass down and printed "nothing" until the build plate got low enough to start printing normal again.