Purple/black circular spot on floor of mouth

Patient: I take suboxone films under my tongue. I’ve been on them for 4 years. This morning a circular purple/black spot appeared on the floor of my mouth. It looks almost perfectly round. It’s on my left side. It doesn’t hurt yet it feels a bit more sensitive. Is this caused by the suboxone? Is this a cause for concern?

Symptoms: Black/purple circular spot on floor of mouth

Images:
Purple/black circular spot ...-1

Doctor: