I shot some stuff on a green screen and used keylight 1.2 in after effects. I accidentally had some green gloves in the shot so I used roto brush to go in and keep them from being keyed out. In the composition preview it looks good; everything that I want kept in is kept in and everything that I want keyed out is keyed out. But after I render it out I get giant chunks of green screen left in the shot. How do stop this from happening?
Also, these are not single frame occurences either, this happen for several seconds.
Your key is not set up accurately enough. It's as simple as that. Keying is not a one click problem. Sometimes you have to adjust nearly every setting in the keyer to pull a good key. Sometimes you even need to use more than one copy of the footage. Many, if not most times you will need to learn how to use garbage mattes.
Your green peaking through is simply a frame where the color values of the part that is showing up are different than the color values of the part that is successfully keyed.