Its not that difficult to reach the bell once you understand how the platforms trigger. It doesn't trigger from you standing on it too long its just a simple looped timer. Each platform will activate a little bit after each other.
There are 4 traversal hook platforming areas in the map and 2 different styles. One with 3 platforms and the one with 2. For the one with 3 platforms wait for your next platform to trigger and use the hook right when it finishes its animation. I noticed that If you try to hook a bit before it you might not actually land on the platform. The one with 2 platforms is a little tricky at first. After getting to the first platform wait for the top platform to trigger. Half way through its animation used the hook and press your 2ndary weapon key when prompted during the swing (spamming the key also seems to work) or you will not reach the platform.
When you reach the bell and ring it, pressing your 2ndary weapon key during the swing will make you let go of the hook. This will prevent you from swinging yourself off the stage.
From what I noticed it takes 3 rings to break his barrier with a full party. It might decrease will less party members?
The message your seeing is just one of his attacks. He only uses it when his barrier is down so it can happen at any time during it. If you want to stop this attack you need to head to the bell asap. During the attack platform traps will never trigger. Also You can only grab on to his leg right when he gets on the ceiling. Do not grab onto his leg if you are the only one up there. Failing to bring him down will kill anyone that grabbed onto him.
At 3 bars the bell will fall. When you reach the top instead of ringing the bell you will cause part of the ceiling to break instead. This can only be trigger once at each platforming area. There is a blue light on the ceiling that indicates which part of the ceils can still break. Breaking the ceiling will light up the center of the stage and when he's in the light his barrier will weaken. You need to do this 3 times at separate locations to break his barrier. He will also take 200~300 damage (every .5s?) when he is in the light.