Blocked drains can be caused by loose vegetation, mildew build up…almost anything.
Leaves and pine needles are the usual culprits outside, while hair and toilet paper may be the problem inside. But this isn’t unusual, these blockages take place as a result of day to day use and simply require maintenance from time to time.
Whatever the case may be, it’s an inconvenience to have blocked drains. You will want the problem to be diagnosed by a qualified plumber and fixed to the best possible standard in a timely fashion.