A common mistake when applying retouching varnish is that the varnish is applied too quickly and excessively.
The solvent of the varnish, if applied on an oil paint that is just hand-dry, will still dissolve some of the oil in the paint, causing the oil to lie on top of the paint and form a sticky layer. If the retouching varnish is used as an intermediate varnish that is then painted over again, there is nothing wrong.
However, if the retouching varnish is applied too quickly as a provisional final varnish, the same phenomenon will occur, resulting in the exterior of the paint film consisting of a mixture of oil and resin. This layer will remain sticky for months and patience is the only solution here.
As this is not the intention, it is advisable to wait a few months before applying the varnish until the paint has dried a little more, at least a month in the case of a very thin paint layer.
Furthermore, it is very important to apply retouching varnish sparingly in all cases. The more varnish, the more solvent is applied and the stronger the problem will be. Moreover, only thin layers of retouching varnish possess sufficient porosity, which is important for the adhesion of subsequent paint layers (intermediate varnish) and for the passage of oxygen for further drying of the paint (provisional final varnish).