Problem:
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  The problem is that InnoDB doesn't add the table in fts slots if drop table fails. InnoDB marks the table is in fts slots while processing sync message. So the consecutive alter statement assumes that table is in queue and tries to remove it. But InnoDB can't find the table in fts_slots.

Solution:
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  i)  Removal of in_queue in fts_t while processing the fts sync message.
  ii) Add the table to fts_slots when drop table fails.