Tub-edge leakage is a common issue in many bathrooms, and homeowners often worry right away that it means the waterproofing has failed.
When it looks more like a sealant issue
If the perimeter sealant has simply aged or a local edge has opened up, and the moisture stays near the visible surface, it may be more of a sealant issue.
When waterproofing or substrate issues should be suspected
If the area becomes wet again soon after resealing, or nearby walls, trim, and base areas also show dampness, the issue may extend beyond the surface.
Why the visible seal line is not enough for diagnosis
Perimeter sealant and internal waterproofing are two different lines of defense. The first is easy to see; the second becomes a deeper issue once it fails.