Conflict can still exist in a world with solid communication and emotional maturity, because some needs are mutually exclusive and we are all limited by material conditions. Observe a living situation with someone who is sensory-seeking and someone who is sensory-avoidant, it's "fun."
Also, no communication is perfect, people misunderstand good intentions on the regular, often behavior is uncontrollably modified by illness, for some differences of opinion there is no objective standard to decide against, we don't always understand what drives our behavior, despite all our scientific advancement we live daily surrounded by things we don't know or understand, even when one is being honest another person can lack trust and disbelieve you, the list goes on and on! So many possibilities!
If your story’s central conflicts depend entirely on people not talking to each other to be a conflict then your conflicts aren’t interesting enough. In real life I have encountered many conflicts, even very messy ones, where open and honest communication does nothing to resolve the issue and everyone is miserable. Where it just fucking sucks and everyone is having a time and talking about it and even reaching mutual empathetic understanding still leaves everyone with no idea what to do.
