Azure OpenAI Assistants suddenly not working properly (both Playground & API)

Question

It seems that something is wrong with recent model roll-outs, affecting Azure OpenAI Assistants.

This is easy to reproduce:

1. Visit Azure AI Foundry -> Azure OpenAI Service -> Playground -> Assistant Playground
2. Create a new Assistant on regions where Assistant preview is available (e.g. sweden, or us east region where Assistant is supported.)
3. Error case 1) Try to change any parameter (e.g. temperature) --> update will fail with strange error message such as "temperature is not supported"
4. Error case 2) try any simple message with the assistant --> this will fail with strange message about either "reasoning_effort", or "stream"
5. Note that
   1. All existing Assistants are affected too -> same errors occur
   2. The results are same also for REST API calls and SDK calls (tested with JAVA SDK beta.5 version)