GPT-5.5 ignores Custom GPT and Project instructions at the start of new chats

GPT-5.5 consistently fails to follow instructions when used in Custom GPTs and Projects.

This happens at the very beginning of every new conversation, not randomly. I already checked that the instructions are not contradictory.

Expected behavior:
GPT-5.5 should follow Custom GPT instructions and Project custom instructions from the first response.

Actual behavior:
The first response already ignores or deviates from those instructions.

Affected areas:

  • Custom GPTs
  • Projects
  • GPT-5.5
  • New conversations

Please investigate whether GPT-5.5 is correctly loading and applying Custom GPT / Project instructions when a new chat starts.