Over time there is loss in vigour and productivity of clones. The phenomenon is known as

Over time there is a loss in vigour and productivity of clones. The phenomenon is known as Clonal degeneration.
The loss in vigour and productivity of clones with time is known as clonal degeneration and it may be due to mutation and infection of viruses and bacteria.
It is when cannabis clones lose their uniqueness in producing certain properties or compounds, including cannabinoids and terpenes.