I've been using Mistral Large 4 and some of my other friends have as well.

Something is going on with the performance (as in speed of the service, not quality). Some days it's quite fast, some days it's so slow I interrupt it because I thought it was hanging.

I think they're shifting hosting capacity around, or otherwise messing with the model. Note that it's still a "preview" version, meaning they're still training it further for the final release and they are likely still figuring out the optimal hosting configuration as well.

It wouldn't surprise me to see further changes in both quality of the model and speed before the final release.