My plums ( not sure what type I have) when growing often secrete a thick sap from the fruit, it does not seem to affect them but
was wondering if this is normal, as my other plum trees do not do this.
Certified GKH Gardening Expert
This can have many causes. In many cases this is no cause for alarm. If this is excessive, or prevents fruit from ripening then it could be an issue that needs treating. This article will help: https://www.gardeningknowhow.com/edible/fruits/plum/plum-tree-is-bleeding-sap.htm