cannot switch to state 15; another operation (2) is in progress

• asyncpg version: 0.23.0
• PostgreSQL version: Aurora PostgreSQL 10.14
• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?: RDS Aurora (and hard to repro)
• Python version: 3.9
• Platform: Linux
• Do you use pgbouncer?: no
• Did you install asyncpg with pip?: pip3.9 install --user
• If you built asyncpg locally, which version of Cython did you use?:
• Can the issue be reproduced under both asyncio and uvloop?: repro'd with uvloop

  File "/root/.local/lib/python3.9/site-packages/asyncpg/pool.py", line 792, in __aexit__
    await self.pool.release(con)
  File "/root/.local/lib/python3.9/site-packages/asyncpg/pool.py", line 666, in release
    return await asyncio.shield(ch.release(timeout))
  File "/usr/lib/python3.9/asyncio/futures.py", line 284, in __await__
    yield self  # This tells Task to wait for completion.
  File "/usr/lib/python3.9/asyncio/tasks.py", line 328, in __wakeup
    future.result()
  File "/usr/lib/python3.9/asyncio/futures.py", line 201, in result
    raise self._exception
  File "/usr/lib/python3.9/asyncio/tasks.py", line 256, in __step
    result = coro.send(None)
  File "/root/.local/lib/python3.9/site-packages/asyncpg/pool.py", line 218, in release
    raise ex
  File "/root/.local/lib/python3.9/site-packages/asyncpg/pool.py", line 208, in release
    await self._con.reset(timeout=budget)
  File "/root/.local/lib/python3.9/site-packages/asyncpg/connection.py", line 1311, in reset
    await self.execute(reset_query, timeout=timeout)
  File "lib/common.py", line 164, in execute
    return await self._with_logger(super(PSQLLoggerMixin, self).execute)(*args, **kwargs)
  File "lib/common.py", line 119, in wrapper
    ret_val = await func(*args, **kwargs)
  File "/root/.local/lib/python3.9/site-packages/asyncpg/connection.py", line 297, in execute
    return await self._protocol.query(query, timeout)
  File "asyncpg/protocol/protocol.pyx", line 338, in query
  File "/usr/lib/python3.9/asyncio/futures.py", line 287, in __await__
    return self.result()  # May raise too.
  File "/usr/lib/python3.9/asyncio/futures.py", line 201, in result
    raise self._exception
  File "asyncpg/protocol/protocol.pyx", line 331, in asyncpg.protocol.protocol.BaseProtocol.query
  File "asyncpg/protocol/coreproto.pyx", line 1061, in asyncpg.protocol.protocol.CoreProtocol._simple_query
  File "asyncpg/protocol/coreproto.pyx", line 768, in asyncpg.protocol.protocol.CoreProtocol._set_state
asyncpg.exceptions._base.InternalClientError: cannot switch to state 15; another operation (2) is in progress

asyncpg/pool.py の release 周辺、asyncpg/connection.py の reset 周辺、asyncpg/protocol/coreproto.pyx の _set_state 周辺から着手してください。traceback を確認し、並行操作の経路を調査してください。報告された問題は再現が難しく、uvloop と Aurora PostgreSQL で発生していたことに注意してください。原因を再現できるか説明でき、接続の解放を壊さずに状態切り替えの失敗を修正できれば完了です。