Operating system: Windows-10-10.0.17763 64 Bits
Graphics card: GeForce GTX 1070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 398.36
Broken: version: 2.80 (sub 74), branch: blender2.7, commit date: 2019-06-06 00:27, hash: rB8b2b79c2108b
Short description of error
When using sewing feature of the cloth simulator, it leaves a gap between sewn vertices. This only happens when Self Collision of the cloth is also on. In Blender 2.79 this is working correctly, i.e. there are no gaps.
Exact steps for others to reproduce the error
With the default cube, delete four side faces ("Only Faces" option, leaving the edges intact). The apply the Cloth modified in the Physics tab and use Sewing with Force 100. You can play the simulation to verify now it works correctly. After checking "Self Collision" and playing the simulation again, there are now gaps.