Well, there's your problem.
GW's plastic glue overall is very, very crappy. All the commission works I've done that have been glued with
gw's plastics have ALL broken down.
The worst case has been, without a doubt, when I accidentally hit the figure case with my foot. It was a slight nudge, and all miniatures were in foam trays waiting for painting. I opened the case, and half of them had some part broken off.
Keep on using that Revell's glue, it's a lot better by far. I use Loctite Super Glue, and it's the best glue I've ever used.