Hi there,
You can have spotting or breakthrough bleeding at any point on T unless you've had a hysterectomy. There is really no rhyme or reason for it, and it's not something you can predict. It seems to occur in most people within the first year on T, but it isn't unheard of for guys who have been on for multiple years to experience it as well.
I would discuss your concerns with your doctor. There is no data to suggest that testosterone use in transgender men causes an increased risk to reproductive cancers. Everybody's body responds to T differently. The change in dose could definitely have something to do with it. It may just be evening itself out after the drop, or you may need to find a dose in between your current one and the old one in order to make it go away.