A bug report does not need a complete diagnosis, but it does need a reproducible observation. Describe where the issue appears, the action taken, the expected result, and the actual result. Include the smallest safe input or sequence that triggers it. State how often it happens and what you have not yet checked.
For example: “On the mobile form, selecting a second image clears the first preview. I expected both to remain. It happened twice on one device; desktop is untested.” That is more actionable than “image upload is broken.” Do not assign a cause until a test distinguishes it from other possibilities. Ask for the next measurement or reproduction step if you cannot narrow it further.
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