When wearing an item with plus to a specific skill, or plus to a category of skills, there is a visual bug that will occur. Having a skill level up, or placing an available point into a skill will trigger this bug. With a + to specific skill item, upon skill level up, it appears as if you lost the +1 to the skill. It will show 0 points available and show the skill at its previous level. However you can still allocate the ‘hidden’ skill point. You can also remove and re-equip the item to correct the UI.
When a single item gives + levels to multiple skills you have specialized, then the visual bug presents slightly differently. It will show say +1 to your three skills it impacts. Once you allocate a skill point to any one of those skills, the +1 disappears from the other skills and it will also say 0 points available. However, you can still allocate said ‘hidden’ skill point.