These soldering wrinkles appeared quite a while ago, but Workingbear recently came across a similar situation on an online forum. Thinking others might encounter the same issue, I decided to document it for both personal reference and to share with everyone.
Workingbear had previously noticed that some data transmission cable samples from a supplier had solder joints on the internal PCBA with wave-like wrinkles and what looked like cracks. At first, it was assumed that these were caused by cracked flux residue. However, even after cleaning the flux with alcohol, the same wave-like wrinkles were still visible, indicating that the issue was actually with the solder itself.