Issues With incoming calls Free PABX

I am receiving complaints about clients dialling our main switchboard number and ending up and random extension number.

I thought this may have been an end user issue with the receptionist but I decided to chan spy on incoming calls and noticed that some clients 1/10 end up directly at random extension numbers.
I have no idea where to start troubleshooting. Any ideas?

With no corroborating information to provide, I doubt many ideas will be forthcoming. Find a log of a call that reflects your suspicion.