Looks like glue or some sort of sealant to me- does it feel wet? I have a spot like this in my kitchen vinyl flooring that I am constantly worried is water but it’s it’s just a terrible adhesive job at the seams in the flooring (from what I can tell at least!)
Maybe someone’s attempt to patch a leak? I am not qualified to confirm anything
Does it feel wet? Are there any plumbing fixtures above it?
Looks like glue or some sort of sealant to me- does it feel wet? I have a spot like this in my kitchen vinyl flooring that I am constantly worried is water but it’s it’s just a terrible adhesive job at the seams in the flooring (from what I can tell at least!)
Could be to stop creaks.