I personally would prefer you admit if you're unsure, but some people would rather you act confident than disclaim.
For the third scenario, "it appears" can be useful, or if more justification is required, "it appears from the (server's behavior|available data|documentation I can find)." Then when you have to correct yourself later, it wasn't you who was misleading, but the situation. I find that this can be used in a completely honest way and often gives non-techy people a more accurate impression of the situation. It helps them understand both the tentative nature of your diagnosis and the obstacles you're struggling with. Win-win.
For the third scenario, "it appears" can be useful, or if more justification is required, "it appears from the (server's behavior|available data|documentation I can find)." Then when you have to correct yourself later, it wasn't you who was misleading, but the situation. I find that this can be used in a completely honest way and often gives non-techy people a more accurate impression of the situation. It helps them understand both the tentative nature of your diagnosis and the obstacles you're struggling with. Win-win.