If you repoint old brickwork with sand and cement mortar, it traps moisture in the bricks. The mortar joints are there to allow water to evaporate through them rather than through the bricks. If the moisture is trapped it will then find its way out through the bricks and with frost action, spall the face of the bricks.
These joints should be repointed with a lime based mortar to allow the wall to breathe.
The render plinth was originally applied to try and keep the damp out. It usually has the opposite effect and traps moisture. Someone then had the bright idea to hack off the lower section to allow the bricks to breath - so far so good; but then went ahead and injected a chemical DPC which was totally unnecessary.
This is what happens to soft bricks when a sand and cement render plinth has been applied. The trapped moisture tries to escape through the brickwork and through frost action causes the face of the bricks to spall. The injected DPC was unnecessary.