I don't have this problem, but reading the posts it is not clear to me whether there is a corner of the tank, or something, in the way, or is it a shelf like board that is obstructing the flow.
If you remove the toilet can you reach the obstruction and see if it some kind of board that has moved and now interferes with the flow?
Removing the toilet is not that big a deal. I have removed mine twice to clean the works when the toilet no longer held water in the bowl.
Good luck!
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