What could cause vaginal bleeding 2 years after a partial hysterectomy?

Needs evaluation. Some people develop extra tissue at the back of the vagina called granulation tissue. This can be removed in the office. If you still have your cervix then some people continue to have light periods. Bleeding 2 years after a hysterectomy needs to be evaluated by your surgeon in the office.
Vaginal atrophy. If menopausal, vaginal bleeding after a hysterectomy may be due to thinning and loss of elasticity of the vaginal walls.
Several. Tears in the vagina are common especially if a person is menopausal without hormone replacement. Sometimes a man has blood in his semen that presents as vaginal bleeding. Other causes include vaginal infections as well as granulation tissuec(scar tissue) in the back of the vagina. Your doctor would need to decide the true cause.
Varies. Yeast, bacterial infection, atrophy, trauma, and cancer are all possibilities. See your doctor for an exam.