A good start to find why would be the journal:
Specifically, journalctl --boot=-1 --priority=3 --catalog
would show all errors or worse in the log of the current session.
If the machine freezes only while running pamac following the log with journalctl --follow
could show if there is a immediate issue specificly while running pamac.
Can you describe in more detail what happens when your system freezes? is it temporary, does mouse movement still happen, can you switch to other active applications etc.