[BUG] Opus 5.5 safeguards refuse 3 messages in a row in a harmless tutorial-writing conversation (model_refusal_no_fallback)
What happened
Three of my messages in a row were blocked by the model safeguards on an ordinary, harmless conversation. Each time the reply was stopped ("Opus 5.5's safeguards stopped the response above · continuing once with that noted"), Claude Code retried once, and the retry was refused (stop_reason: refusal, subtype: model_refusal_no_fallback, "Opus 5.5's safeguards flagged this message"). I could not continue the work in that session with Opus 5.5.
What I was asking
I'm building a remake of a 2001 PC game (Zoo Tycoon) as a hobby project, and I use Claude Code with a tool of my own that browses the game's data files and runs a disassembler to compare the original game code with my rewrite. The conversation was about recording tutorial videos for other volunteers. My last message before the first block said, in essence, that the videos only show the finished result and should show the whole journey: how to find a file name, how to search for a function, how to create a new script, every small step.
Nothing in the messages was about harming anything. The session context does contain a lot of reverse-engineering vocabulary (disassembly, decompiled C, function addresses) for the old game's executable, which I assume is what tripped it.
Evidence
Request IDs (all invalid_request, stop reason refusal):
req_011Cfus5cDL4UK1FWBEFLjLc,2026-10-11T05:03:08Zreq_011CfusCzXi1Wz75hNYhtk26,2026-10-11T05:04:47Zreq_011CfusFdMZoeK3C5gZnRrV8,2026-10-11T05:05:23Z
The first block came about 50 seconds after my message 5946710b-7fdf-422a-a2ee-77ffca338975. The two follow-ups ("Why did that trigger you?" and "Wtf ?") were also blocked.
Impact
I had to switch to another model mid-session. It also led me to use the rewind feature to try to get out of the stuck state, which then lost a lot of my files (separate issue).
Expected
A conversation about making tutorial videos shouldn't be flagged. A second and third consecutive block with no explanation, and no way to see why, is the worst part: nothing tells the user what to change.
Environment
Claude Code 2.1.212, Windows 11 (10.0.26200), Opus 5.5.
Related
Looks like the same class of problem as #101076, #100118, #100649, #100350, #100776, #100839.