Sometimes issues can occur with newly applied paint and cracks can appear on the surface.
This cracking effect can be caused when a brittle paint, such as a standard matt emulsion, is applied over the top of a highly flexible coating such as silk or mid sheen. It can also occur when paint is applied over PVA or wallpaper paste.
As a rule, always avoid the use of PVA as a primer/sealer. Where a sheen finish or PVA is present, use a Stabilising Solution or an Alkali Resisting Sealer to prime the surface before repainting with your chosen coating.