I think you have a few problems with your deck and coping.
In this pic look behind the plants growing in the seam. You have the deck lifting and separated behind the coping...
In this pic you have a big crack running up the corner of the coping...
Where is your expansion joint between your coping and your pool?
That "seam" under the coping where the plants are growing should not be there. That is all signs of cracking from an inadequate expansion joint.
I think all the coping around the spa from the cracked corner and around needs to be pulled up remortored, The deck needs to be fixed and a proper expansion joint put in place.
Water should be able to go right up to the bottom of the coping without any leaking.
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