.380 Guardian

[jmom54]

Hi. I'm new to this forum. I recently cleaned my .380 Guardian and after reassembling it, when I pull the slide back it lifts up in the back and the small button that releases the slide for cleaning falls out. I have cleaned this pistol before  with out having this happen.
Could anybody have an idea why this is happening? I'm puzzled and hope one of you can tell me why this is happening.

Thanks alot
jmom