Parachutes don't open after staging

Hi, I have a rocket with several boosters. I've placed parachutes and a command disk at the top of the boosters so as to recover them once they are removed by staging. After staging, if I switch to one of the boosters, i can see that the parachutes which are activated upon staging are activated and open at the appropriate altitude/speed. However, if I stay focused on the main rocket, the boosters just disappear at some point and I can't recover them. Not sure what's going on. Happy to send you an example rocket if that would help.
best
Ruben