Bedrock Agents replaces user message with duplicated tool_result after tool invocation

I’m experiencing a recurring issue with AWS Bedrock Agents where the user’s original message disappears from the conversation history and is replaced by the tool_result, which also gets duplicated.

✅ Expected behavior After a tool call, the user message should remain in the trace.

"messages": [
  {
    "role": "user",
    "content": "[{text='Hola buenas noches. Quisiera sacar cita con Adriana Gamarra.', type=text}]"
  },
  {
    "role": "assistant",
    "content": "[{text='<thinking>Verificar si la doctora existe</thinking>', type=text}, {input={gender='Femenino', full_names=['Adriana Gamarra']}, name='schedule__get_health_worker_ids', type='tool_use'}]"
  },
  {
    "role": "user",
    "content": "[{tool_use_id='toolu_bdrk_01Ah7KiyXfEwuDCnGZ3fwB9x', type='tool_result', content='[{\"id\":2,\"full_name\":\"Adriana Gamarra Luna\",\"specialty\":\"Dermatología\",\"consultation_fee\":\"S/ 250\"}]'}]"
  }
]

❌ Actual behavior After the tool_result, the original user message is replaced by the same tool_result, duplicated:

"messages": [
  {
    "role": "user",
    "content": "[{text='[{\"id\":164,\"full_name\":\"Adriana Gamarra Luna\",\"specialty\":\"Dermatologia\",\"consultation_fee\":\"S/ 250\"}]', type=text}]"
  },
  {
    "role": "assistant",
    "content": "[{text='<thinking>Voy a saludar y buscar el ID de la Dra. Adriana Gamarra...</thinking>', type=text}, {input={gender='Femenino', full_names=['Adriana Gamarra']}, name='schedule__get_health_worker_ids', type='tool_use'}]"
  },
  {
    "role": "user",
    "content": "[{tool_use_id='toolu_bdrk_01AGKbao3BvvXTjVhaVirjY7', type='tool_result', content='[{\"id\":164,\"full_name\":\"Adriana Gamarra Luna\",\"specialty\":\"Dermatologia\",\"consultation_fee\":\"S/ 250\"}]'}]"
  }
]

You can see that the first user message (the greeting and intent) was replaced by the tool_result JSON. As a result, the agent loses context and responds incoherently (it thinks the user sent structured data instead of text).

Environment

• Models tested: Claude Sonnet 3.5 , 3.7 y 4.5
• Regions: us-east-1 (Virginia)
• Happens both in: Bedrock agent Console test chat and SDK (PHP)
• Agent config: User input enabled, Action groups,1 Knowledge Bases, Orchestration strategy (only "Orchestration" default)
• Started happening: October 23, 2025

Is anyone else experiencing this issue? It seems related to session state corruption, but there’s no report on AWS Health about it.