Bathroom
If it only happens during a shower, write that down.
A downstairs stain that appears mid-shower is one of the clearer patterns in stacked bathrooms. It still needs a source, because tile, pans, valves, and waste lines each fail differently.
Stop using that shower until the path is known.
Continuing to test it ‘one more time’ adds water to someone else’s ceiling. Use another fixture if the building can offer one.
Grout is not always the villain.
Missing grout can let water in. So can a failed membrane, an unsealed fixture, or a valve in the wall. A camera at the drain is not a full answer either.
Coordinate both bathrooms.
The investigator needs the upstairs shower and the downstairs ceiling in the same visit when possible. Separate appointments waste the pattern.
Questions people ask
Can I recaulk and hope?
Fresh caulk can hide an active leak long enough to damage the suite below. Get the path named first.
Is this common-property or the unit?
That is a corporation question. The physical finding should be written so the corporation can apply its documents. ProShield does not decide bylaws.