Just began brewing in January, started with kits but have switched to all grain for the last 6 batches. The first 4 AG beers came out acceptable (with obvious room for improvement) but no red flags. However, the last 2 batches turn flat after I refrigerate them, even a month after bottling. If they're poured at room temperature without any chilling prior there is no problem; 1/2-1" head and good carbonation. It's like a chill haze but with carbonation. Any suggestions? This has been really frustrating, any help or insight would be really appreciated, thanks!