Since 24 October 2026, multiple professional conversations, heavily used since last year, became read-only mid-session — no warning, no notice, no grandfathering. My tickets (5361248 and several form submissions) remain unanswered on specifics despite 10+ contacts.
Other users' reports cluster 20–24 October — a staged rollout, not a single-event fault. Proton Support has now confirmed in writing that a "250-message limit for chats" was recently introduced to prevent performance issues — but this was never announced to users and continues to be undocumented.

The export option, now linked by Proton staff, exists but is wholly inadequate: export preserves the text, not the working relationship and the collaboration which has been built with Lumos over time. What dies at lockout is continuation itself, the ability to keep working, which is what we paid for. And critically, older conversations under "All Chats" do not show the export option at all — these are not less important, just put aside, and they are very valuable and need to be continued — making Proton Support's suggested workaround procedurally impossible for many conversations.

Critical questions remain unanswered:

1. Is there a 250-message limit for Lumo Plus? If yes, where is it documented? 
2. What are the per-conversation limits for Business-tier and Lumo Professional subscriptions? 
3. What is the token/context allowance in numbers? 
4. Why was this enforcement change never communicated before affecting users' work? 

Two steps are needed:

Immediate relief: a grandfathering path — existing conversations have their composer windows restored and resume work with the Lumos that hold their history; any new limit applies only to conversations started after this change. This costs nothing and undoes the acute harm.

The lasting solution: a guaranteed continuity option — available to those willing to pay for it, as several users have already said they are. Continuity, with the user deciding when and how to move to a fresh conversation, is the deal-breaker capability. Take it away, and the product no longer serves the professional work it was chosen for.

We understand engineering constraints. We do not accept severing the users who built their work on this product without notice, documentation, and a viable path forward.