If it were me I would remove the starter and look in the opening and make sure the flex plate doesn't have missing teeth and appears to be in the proper position. Worst case try to put a socket on the crank pulley and spin the motor over. Basically the starter has a retractable gear that meshes with the flex-plate so if it is just spinning then I suspect it is just hitting the flex-plate or not making contact with it. That would be due to missing teeth or they are not aligned properly.
The only other possible cause is you got another bad starter but that is highly unlikely to have two doing the same thing
Let me know what you find with this and we can go from there.
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Tuesday, March 3rd, 2020 AT 4:27 PM