870 forearm slides out of the receiver

[Snirunner24]

My 870 forearm slides out of the receiver without pressing in the catches on the inside. I know it's not really a problem if the barrel is installed but when racking fast with the barrel on the arms seem to bind a little and makes it harder to rack. I have another 870 and swapped the forearms with the same results. So it has to be in the receiver itself. I've had the gun for 20 years and purchased it on my 18th birthday so I would really like to keep it running right.